Steps to reproduce the issue

1. Create an extension and load an editor in it (for exemple AcyMailing) with custom config
2. Select TinyMCE as the default editor in Joomla configuration
3. Go to the TinyMCE plugin settings and save the form (you don't have to change anything)
4. Load the editor in the plugin (in AcyMailing create a new template with the website editor, save it and then refresh it)

Expected result

Displays TinyMCE editor

Actual result

PHP Fatal error

System information (as much as possible)

Fatal error: Attempt to assign property "joomlaBrokeItInAMinorRelease" on array

Call stack
--
# | Function | Location
1 | () | JROOT/libraries/vendor/joomla/registry/src/Registry.php:766
2 | Joomla\Registry\Registry->bindData() | JROOT/libraries/vendor/joomla/registry/src/Registry.php:761
3 | Joomla\Registry\Registry->bindData() | JROOT/libraries/vendor/joomla/registry/src/Registry.php:761
4 | Joomla\Registry\Registry->bindData() | JROOT/libraries/vendor/joomla/registry/src/Registry.php:278
5 | Joomla\Registry\Registry->loadArray() | JROOT/libraries/src/Editor/Editor.php:298
6 | Joomla\CMS\Editor\Editor->_loadEditor() | JROOT/libraries/src/Editor/Editor.php:170
7 | Joomla\CMS\Editor\Editor->display() | JROOT/administrator/components/com_acym/helpers/editor.php:165
8 | AcyMailing\Helpers\EditorHelper->displayJoomla() | JROOT/administrator/components/com_acym/helpers/editor.php:83
9 | AcyMailing\Helpers\EditorHelper->display() | JROOT/administrator/components/com_acym/views/mails/tmpl/edit.php:41
10 | include() | JROOT/administrator/components/com_acym/libraries/view.php:113
11 | AcyMailing\Libraries\acymView->display() | JROOT/administrator/components/com_acym/libraries/controller.php:210
12 | AcyMailing\Libraries\acymController->display() | JROOT/administrator/components/com_acym/controllers/mails.php:450
13 | AcyMailing\Controllers\MailsController->edit() | JROOT/administrator/components/com_acym/libraries/controller.php:104
14 | AcyMailing\Libraries\acymController->call() | JROOT/administrator/components/com_acym/acym.php:73
15 | require_once() | JROOT/libraries/src/Dispatcher/LegacyComponentDispatcher.php:71
16 | Joomla\CMS\Dispatcher\LegacyComponentDispatcher::Joomla\CMS\Dispatcher\{closure}() | JROOT/libraries/src/Dispatcher/LegacyComponentDispatcher.php:73
17 | Joomla\CMS\Dispatcher\LegacyComponentDispatcher->dispatch() | JROOT/libraries/src/Component/ComponentHelper.php:355
18 | Joomla\CMS\Component\ComponentHelper::renderComponent() | JROOT/libraries/src/Application/AdministratorApplication.php:143
19 | Joomla\CMS\Application\AdministratorApplication->dispatch() | JROOT/libraries/src/Application/AdministratorApplication.php:186
20 | Joomla\CMS\Application\AdministratorApplication->doExecute() | JROOT/libraries/src/Application/CMSApplication.php:294
21 | Joomla\CMS\Application\CMSApplication->execute() | JROOT/administrator/includes/app.php:61
22 | require_once() | JROOT/administrator/index.php:32

Additional comments

The error only appear when you load TinyMCE with custom parameters and you already save the TinyMCE settings.
For exemple in AcyMailing we add a custom config to TinyMCE to add custom CSS to the render, we do it in the file administrator/components/com_acym/helpers/editor.php with this structure:

$this->editorConfig['configuration'] = (object)[
                    'toolbars' => (object)['joomlaBrokeItInAMinorRelease' => []],
                    'setoptions' => [
                        'joomlaBrokeItInAMinorRelease' => (object)[
                            'access' => $access,
                            'content_css' => '0',
                            'content_css_custom' => $cssurl.'&local=http',
                        ],
                    ],
                ];

The fatal happens in libraries/vendor/joomla/registry/src/Registry.php:766 in the bind function because it tries to assign an object key to an array.
The error comes from when we save the TinyMCE plugin settings, it transform the params from an object to an array.
I've tested it on Joomla 3 and after saving the TinyMCE plugin settings it work.