Steps to reproduce the issue

use php 8
go to Admin->Control Panel

Expected result

no warning

Actual result

[21-Nov-2020 08:46:20 UTC] PHP Warning:  FOFModelBehavior::onBeforeBuildQuery(): Argument #1 ($model) must be passed by reference, value given in /shared/httpd/joomla3/joomla-cms-staging/libraries/fof/utils/observable/event.php on line 63
[21-Nov-2020 08:46:20 UTC] PHP Stack trace:
[21-Nov-2020 08:46:20 UTC] PHP   1. {main}() /shared/httpd/joomla3/joomla-cms-staging/administrator/index.php:0
[21-Nov-2020 08:46:20 UTC] PHP   2. Joomla\CMS\Application\AdministratorApplication->execute() /shared/httpd/joomla3/joomla-cms-staging/administrator/index.php:51
[21-Nov-2020 08:46:20 UTC] PHP   3. Joomla\CMS\Application\AdministratorApplication->doExecute() /shared/httpd/joomla3/joomla-cms-staging/libraries/src/Application/CMSApplication.php:196
[21-Nov-2020 08:46:20 UTC] PHP   4. Joomla\CMS\Application\AdministratorApplication->dispatch($component = *uninitialized*) /shared/httpd/joomla3/joomla-cms-staging/libraries/src/Application/AdministratorApplication.php:159
[21-Nov-2020 08:46:20 UTC] PHP   5. Joomla\CMS\Component\ComponentHelper::renderComponent($option = 'com_cpanel', $params = *uninitialized*) /shared/httpd/joomla3/joomla-cms-staging/libraries/src/Application/AdministratorApplication.php:101
[21-Nov-2020 08:46:20 UTC] PHP   6. Joomla\CMS\Component\ComponentHelper::executeComponent($path = '/shared/httpd/joomla3/joomla-cms-staging/administrator/components/com_cpanel/cpanel.php') /shared/httpd/joomla3/joomla-cms-staging/libraries/src/Component/ComponentHelper.php:377
[21-Nov-2020 08:46:20 UTC] PHP   7. require_once() /shared/httpd/joomla3/joomla-cms-staging/libraries/src/Component/ComponentHelper.php:402
[21-Nov-2020 08:46:20 UTC] PHP   8. CpanelController->execute($task = NULL) /shared/httpd/joomla3/joomla-cms-staging/administrator/components/com_cpanel/cpanel.php:15
[21-Nov-2020 08:46:20 UTC] PHP   9. CpanelController->display($cachable = *uninitialized*, $urlparams = *uninitialized*) /shared/httpd/joomla3/joomla-cms-staging/libraries/src/MVC/Controller/BaseController.php:710
[21-Nov-2020 08:46:20 UTC] PHP  10. CpanelViewCpanel->display($tpl = *uninitialized*) /shared/httpd/joomla3/joomla-cms-staging/libraries/src/MVC/Controller/BaseController.php:672
[21-Nov-2020 08:46:20 UTC] PHP  11. PostinstallModelMessages->getItemList($overrideLimits = *uninitialized*, $group = *uninitialized*) /shared/httpd/joomla3/joomla-cms-staging/administrator/components/com_cpanel/views/cpanel/view.html.php:53
[21-Nov-2020 08:46:20 UTC] PHP  12. PostinstallModelMessages->buildQuery($overrideLimits = FALSE) /shared/httpd/joomla3/joomla-cms-staging/libraries/fof/model/model.php:1221
[21-Nov-2020 08:46:20 UTC] PHP  13. PostinstallModelMessages->buildQuery($overrideLimits = FALSE) /shared/httpd/joomla3/joomla-cms-staging/administrator/components/com_postinstall/models/messages.php:30
[21-Nov-2020 08:46:20 UTC] PHP  14. FOFModelDispatcherBehavior->trigger($event = 'onBeforeBuildQuery', $args = [0 => class PostinstallModelMessages { protected $__state_set = NULL; protected $_db = class FOFDatabaseDriverJoomla { ... }; protected $event_after_delete = 'onContentAfterDelete'; protected $event_after_save = 'onContentAfterSave'; protected $event_before_delete = 'onContentBeforeDelete'; protected $event_before_save = 'onContentBeforeSave'; protected $event_change_state = 'onContentChangeState'; protected $event_clean_cache = NULL; protected $id_list = NULL; protected $id = 0; protected $input = class FOFInput { ... }; protected $list = NULL; protected $name = 'messages'; protected $option = 'com_postinstall'; protected $otable = NULL; protected $pagination = NULL; protected $record = NULL; protected $state = class FOFUtilsObject { ... }; protected $table = 'message'; protected $total = NULL; protected $_savestate = FALSE; protected $_forms = [...]; protected $_formData = [...]; protected $configProvider = class FOFConfigProvider { ... }; protected $modelDispatcher = class FOFModelDispatcherBehavior { ... }; protected $default_behaviors = [...]; protected $_behaviorParams = [...]; protected $_errors = [...] }, 1 => class JDatabaseQueryPdomysql { protected $offset = NULL; protected $limit = NULL; protected $db = class JDatabaseDriverPdomysql { ... }; protected $sql = NULL; protected $type = ''; protected $element = NULL; protected $select = NULL; protected $delete = NULL; protected $update = NULL; protected $insert = NULL; protected $from = NULL; protected $join = NULL; protected $set = NULL; protected $where = NULL; protected $group = NULL; protected $having = NULL; protected $columns = NULL; protected $values = NULL; protected $order = NULL; protected $autoIncrementField = NULL; protected $call = NULL; protected $exec = NULL; protected $union = NULL; protected $unionAll = NULL; protected $selectRowNumber = NULL }]) /shared/httpd/joomla3/joomla-cms-staging/libraries/fof/model/model.php:2071
[21-Nov-2020 08:46:20 UTC] PHP  15. FOFModelBehaviorFilters->update($args = [0 => class PostinstallModelMessages { protected $__state_set = NULL; protected $_db = class FOFDatabaseDriverJoomla { ... }; protected $event_after_delete = 'onContentAfterDelete'; protected $event_after_save = 'onContentAfterSave'; protected $event_before_delete = 'onContentBeforeDelete'; protected $event_before_save = 'onContentBeforeSave'; protected $event_change_state = 'onContentChangeState'; protected $event_clean_cache = NULL; protected $id_list = NULL; protected $id = 0; protected $input = class FOFInput { ... }; protected $list = NULL; protected $name = 'messages'; protected $option = 'com_postinstall'; protected $otable = NULL; protected $pagination = NULL; protected $record = NULL; protected $state = class FOFUtilsObject { ... }; protected $table = 'message'; protected $total = NULL; protected $_savestate = FALSE; protected $_forms = [...]; protected $_formData = [...]; protected $configProvider = class FOFConfigProvider { ... }; protected $modelDispatcher = class FOFModelDispatcherBehavior { ... }; protected $default_behaviors = [...]; protected $_behaviorParams = [...]; protected $_errors = [...] }, 1 => class JDatabaseQueryPdomysql { protected $offset = NULL; protected $limit = NULL; protected $db = class JDatabaseDriverPdomysql { ... }; protected $sql = NULL; protected $type = ''; protected $element = NULL; protected $select = NULL; protected $delete = NULL; protected $update = NULL; protected $insert = NULL; protected $from = NULL; protected $join = NULL; protected $set = NULL; protected $where = NULL; protected $group = NULL; protected $having = NULL; protected $columns = NULL; protected $values = NULL; protected $order = NULL; protected $autoIncrementField = NULL; protected $call = NULL; protected $exec = NULL; protected $union = NULL; protected $unionAll = NULL; protected $selectRowNumber = NULL }]) /shared/httpd/joomla3/joomla-cms-staging/libraries/fof/utils/observable/dispatcher.php:146
[21-Nov-2020 08:46:20 UTC] PHP Warning:  FOFModelBehaviorFilters::onAfterBuildQuery(): Argument #1 ($model) must be passed by reference, value given in /shared/httpd/joomla3/joomla-cms-staging/libraries/fof/utils/observable/event.php on line 63
[21-Nov-2020 08:46:20 UTC] PHP Stack trace:
[21-Nov-2020 08:46:20 UTC] PHP   1. {main}() /shared/httpd/joomla3/joomla-cms-staging/administrator/index.php:0
[21-Nov-2020 08:46:20 UTC] PHP   2. Joomla\CMS\Application\AdministratorApplication->execute() /shared/httpd/joomla3/joomla-cms-staging/administrator/index.php:51
[21-Nov-2020 08:46:20 UTC] PHP   3. Joomla\CMS\Application\AdministratorApplication->doExecute() /shared/httpd/joomla3/joomla-cms-staging/libraries/src/Application/CMSApplication.php:196
[21-Nov-2020 08:46:20 UTC] PHP   4. Joomla\CMS\Application\AdministratorApplication->dispatch($component = *uninitialized*) /shared/httpd/joomla3/joomla-cms-staging/libraries/src/Application/AdministratorApplication.php:159
[21-Nov-2020 08:46:20 UTC] PHP   5. Joomla\CMS\Component\ComponentHelper::renderComponent($option = 'com_cpanel', $params = *uninitialized*) /shared/httpd/joomla3/joomla-cms-staging/libraries/src/Application/AdministratorApplication.php:101
[21-Nov-2020 08:46:20 UTC] PHP   6. Joomla\CMS\Component\ComponentHelper::executeComponent($path = '/shared/httpd/joomla3/joomla-cms-staging/administrator/components/com_cpanel/cpanel.php') /shared/httpd/joomla3/joomla-cms-staging/libraries/src/Component/ComponentHelper.php:377
[21-Nov-2020 08:46:20 UTC] PHP   7. require_once() /shared/httpd/joomla3/joomla-cms-staging/libraries/src/Component/ComponentHelper.php:402
[21-Nov-2020 08:46:20 UTC] PHP   8. CpanelController->execute($task = NULL) /shared/httpd/joomla3/joomla-cms-staging/administrator/components/com_cpanel/cpanel.php:15
[21-Nov-2020 08:46:20 UTC] PHP   9. CpanelController->display($cachable = *uninitialized*, $urlparams = *uninitialized*) /shared/httpd/joomla3/joomla-cms-staging/libraries/src/MVC/Controller/BaseController.php:710
[21-Nov-2020 08:46:20 UTC] PHP  10. CpanelViewCpanel->display($tpl = *uninitialized*) /shared/httpd/joomla3/joomla-cms-staging/libraries/src/MVC/Controller/BaseController.php:672
[21-Nov-2020 08:46:20 UTC] PHP  11. PostinstallModelMessages->getItemList($overrideLimits = *uninitialized*, $group = *uninitialized*) /shared/httpd/joomla3/joomla-cms-staging/administrator/components/com_cpanel/views/cpanel/view.html.php:53
[21-Nov-2020 08:46:20 UTC] PHP  12. PostinstallModelMessages->buildQuery($overrideLimits = FALSE) /shared/httpd/joomla3/joomla-cms-staging/libraries/fof/model/model.php:1221
[21-Nov-2020 08:46:20 UTC] PHP  13. PostinstallModelMessages->buildQuery($overrideLimits = FALSE) /shared/httpd/joomla3/joomla-cms-staging/administrator/components/com_postinstall/models/messages.php:30
[21-Nov-2020 08:46:20 UTC] PHP  14. FOFModelDispatcherBehavior->trigger($event = 'onAfterBuildQuery', $args = [0 => class PostinstallModelMessages { protected $__state_set = TRUE; protected $_db = class FOFDatabaseDriverJoomla { ... }; protected $event_after_delete = 'onContentAfterDelete'; protected $event_after_save = 'onContentAfterSave'; protected $event_before_delete = 'onContentBeforeDelete'; protected $event_before_save = 'onContentBeforeSave'; protected $event_change_state = 'onContentChangeState'; protected $event_clean_cache = NULL; protected $id_list = NULL; protected $id = 0; protected $input = class FOFInput { ... }; protected $list = NULL; protected $name = 'messages'; protected $option = 'com_postinstall'; protected $otable = NULL; protected $pagination = NULL; protected $record = NULL; protected $state = class FOFUtilsObject { ... }; protected $table = 'message'; protected $total = NULL; protected $_savestate = FALSE; protected $_forms = [...]; protected $_formData = [...]; protected $configProvider = class FOFConfigProvider { ... }; protected $modelDispatcher = class FOFModelDispatcherBehavior { ... }; protected $default_behaviors = [...]; protected $_behaviorParams = [...]; protected $_errors = [...] }, 1 => class JDatabaseQueryPdomysql { protected $offset = NULL; protected $limit = NULL; protected $db = class JDatabaseDriverPdomysql { ... }; protected $sql = NULL; protected $type = 'select'; protected $element = NULL; protected $select = class JDatabaseQueryElement { ... }; protected $delete = NULL; protected $update = NULL; protected $insert = NULL; protected $from = class JDatabaseQueryElement { ... }; protected $join = NULL; protected $set = NULL; protected $where = NULL; protected $group = NULL; protected $having = NULL; protected $columns = NULL; protected $values = NULL; protected $order = class JDatabaseQueryElement { ... }; protected $autoIncrementField = NULL; protected $call = NULL; protected $exec = NULL; protected $union = NULL; protected $unionAll = NULL; protected $selectRowNumber = NULL }]) /shared/httpd/joomla3/joomla-cms-staging/libraries/fof/model/model.php:2115
[21-Nov-2020 08:46:20 UTC] PHP  15. FOFModelBehaviorFilters->update($args = [0 => class PostinstallModelMessages { protected $__state_set = TRUE; protected $_db = class FOFDatabaseDriverJoomla { ... }; protected $event_after_delete = 'onContentAfterDelete'; protected $event_after_save = 'onContentAfterSave'; protected $event_before_delete = 'onContentBeforeDelete'; protected $event_before_save = 'onContentBeforeSave'; protected $event_change_state = 'onContentChangeState'; protected $event_clean_cache = NULL; protected $id_list = NULL; protected $id = 0; protected $input = class FOFInput { ... }; protected $list = NULL; protected $name = 'messages'; protected $option = 'com_postinstall'; protected $otable = NULL; protected $pagination = NULL; protected $record = NULL; protected $state = class FOFUtilsObject { ... }; protected $table = 'message'; protected $total = NULL; protected $_savestate = FALSE; protected $_forms = [...]; protected $_formData = [...]; protected $configProvider = class FOFConfigProvider { ... }; protected $modelDispatcher = class FOFModelDispatcherBehavior { ... }; protected $default_behaviors = [...]; protected $_behaviorParams = [...]; protected $_errors = [...] }, 1 => class JDatabaseQueryPdomysql { protected $offset = NULL; protected $limit = NULL; protected $db = class JDatabaseDriverPdomysql { ... }; protected $sql = NULL; protected $type = 'select'; protected $element = NULL; protected $select = class JDatabaseQueryElement { ... }; protected $delete = NULL; protected $update = NULL; protected $insert = NULL; protected $from = class JDatabaseQueryElement { ... }; protected $join = NULL; protected $set = NULL; protected $where = NULL; protected $group = NULL; protected $having = NULL; protected $columns = NULL; protected $values = NULL; protected $order = class JDatabaseQueryElement { ... }; protected $autoIncrementField = NULL; protected $call = NULL; protected $exec = NULL; protected $union = NULL; protected $unionAll = NULL; protected $selectRowNumber = NULL }]) /shared/httpd/joomla3/joomla-cms-staging/libraries/fof/utils/observable/dispatcher.php:146

System information (as much as possible)

php 8
jooomla 3 staging/rc