Steps to reproduce the issue

Change "administrator" folder in "/includes/defines.php" and "/administrator/includes/defines.php" to "admin"
rename "administrator" folder to "admin"

Expected result

Everything working

Actual result

Fields not getting loaded due to wrong path

System information (as much as possible)

Joomla 5.x

Additional comments

Fix paths in the "prepareForm" function in administrator/components/com_fields/src/Helper/FieldsHelper.php lines 430 and 431.

CURRENT CODE

$fieldset->setAttribute('addfieldpath', '/administrator/components/' . $component . '/models/fields');
$fieldset->setAttribute('addrulepath', '/administrator/components/' . $component . '/models/rules');

PROPOSED FIX

$fieldset->setAttribute('addfieldpath', str_replace(JPATH_ROOT, '', JPATH_ADMINISTRATOR) . '/components/' . $component . '/models/fields');
$fieldset->setAttribute('addrulepath', str_replace(JPATH_ROOT, '', JPATH_ADMINISTRATOR) . '/components/' . $component . '/models/rules');

Related

Related to issue #44980