Oauth2 client identifier is not a valid attribute

Hello Nextcloud people!
I just migrated my Owncloud 10.5.0 to Nextcloud 20.0.4 and have a problem I can’t solve on my own. Except two errors, which I was able to fix with the help of the forum, Nextcloud is running. But it is not possible to open the security site under administration. I’m just getting an “Internal Server Error” error screen. The corresponding error log is the following:

{“reqId”:“VwPXtZFFQAK7jWFfC3Ad”,“level”:3,“time”:“2021-06-04T10:15:35+00:00”,“remoteAddr”:“83.135.168.18”,“user”:“zinkenmartin”,“app”:“index”,“method”:“GET”,“url”:"/owncloud/index.php/settings/admin/security",“message”:{“Exception”:“BadFunctionCallException”,“Message”:“identifier is not a valid attribute”,“Code”:0,“Trace”:[{“file”:"/var/www/owncloud/lib/public/AppFramework/Db/Entity.php",“line”:151,“function”:“setter”,“class”:“OCP\AppFramework\Db\Entity”,“type”:"->",“args”:[“identifier”,[“Y6jMfXpkdfi…”]]},{“file”:"/var/www/owncloud/lib/public/AppFramework/Db/Entity.php",“line”:73,“function”:"__call",“class”:“OCP\AppFramework\Db\Entity”,“type”:"->",“args”:[“setIdentifier”,[“Y6jMfXpkdfi…”]]},{“file”:"/var/www/owncloud/lib/public/AppFramework/Db/QBMapper.php",“line”:307,“function”:“fromRow”,“class”:“OCP\AppFramework\Db\Entity”,“type”:"::",“args”:[{“id”:“4”,“identifier”:“Y6jMfXpkdfi…”,“secret”:“mziegQBrhPvx…”,“redirect_uri”:“https://meinedomain.com:4443/owncloud/index.php/apps/oauth2/api/v1/token",“name”:"Access Token URL”,“allow_subdomains”:“0”}]},{“file”:"/var/www/owncloud/lib/public/AppFramework/Db/QBMapper.php",“line”:325,“function”:“mapRowToEntity”,“class”:“OCP\AppFramework\Db\QBMapper”,“type”:"->",“args”:[{“id”:“4”,“identifier”:“Y6jMfXpkdfi…”,“secret”:“mziegQBrhPvx…”,“redirect_uri”:“https://meinedomain.com:4443/owncloud/index.php/apps/oauth2/api/v1/token",“name”:"Access Token URL”,“allow_subdomains”:“0”}]},{“file”:"/var/www/owncloud/apps/oauth2/lib/Db/ClientMapper.php",“line”:95,“function”:“findEntities”,“class”:“OCP\AppFramework\Db\QBMapper”,“type”:"->",“args”:[{“class”:“OC\DB\QueryBuilder\QueryBuilder”}]},{“file”:"/var/www/owncloud/apps/oauth2/lib/Settings/Admin.php",“line”:50,“function”:“getClients”,“class”:“OCA\OAuth2\Db\ClientMapper”,“type”:"->",“args”:},{“file”:"/var/www/owncloud/apps/settings/lib/Controller/CommonSettingsTrait.php",“line”:141,“function”:“getForm”,“class”:“OCA\OAuth2\Settings\Admin”,“type”:"->",“args”:},{“file”:"/var/www/owncloud/apps/settings/lib/Controller/AdminSettingsController.php",“line”:83,“function”:“formatSettings”,“class”:“OCA\Settings\Controller\AdminSettingsController”,“type”:"->",“args”:[{“10”:[{“class”:“OCA\Settings\Settings\Admin\Security”}],“50”:[{“class”:“OCA\Password_Policy\Settings”},{“class”:“OCA\BruteForceSettings\Settings\IPWhitelist”}],“100”:[{“class”:“OCA\OAuth2\Settings\Admin”}]}]},{“file”:"/var/www/owncloud/apps/settings/lib/Controller/CommonSettingsTrait.php",“line”:152,“function”:“getSettings”,“class”:“OCA\Settings\Controller\AdminSettingsController”,“type”:"->",“args”:[“security”]},{“file”:"/var/www/owncloud/apps/settings/lib/Controller/AdminSettingsController.php",“line”:68,“function”:“getIndexResponse”,“class”:“OCA\Settings\Controller\AdminSettingsController”,“type”:"->",“args”:[“admin”,“security”]},{“file”:"/var/www/owncloud/lib/private/AppFramework/Http/Dispatcher.php",“line”:169,“function”:“index”,“class”:“OCA\Settings\Controller\AdminSettingsController”,“type”:"->",“args”:[“security”]},{“file”:"/var/www/owncloud/lib/private/AppFramework/Http/Dispatcher.php",“line”:100,“function”:“executeController”,“class”:“OC\AppFramework\Http\Dispatcher”,“type”:"->",“args”:[{“class”:“OCA\Settings\Controller\AdminSettingsController”},“index”]},{“file”:"/var/www/owncloud/lib/private/AppFramework/App.php",“line”:152,“function”:“dispatch”,“class”:“OC\AppFramework\Http\Dispatcher”,“type”:"->",“args”:[{“class”:“OCA\Settings\Controller\AdminSettingsController”},“index”]},{“file”:"/var/www/owncloud/lib/private/Route/Router.php",“line”:308,“function”:“main”,“class”:“OC\AppFramework\App”,“type”:"::",“args”:[“OCA\Settings\Controller\AdminSettingsController”,“index”,{“class”:“OC\AppFramework\DependencyInjection\DIContainer”},{“section”:“security”,“action”:null,"_route":“settings.AdminSettings.index”}]},{“file”:"/var/www/owncloud/lib/base.php",“line”:1008,“function”:“match”,“class”:“OC\Route\Router”,“type”:"->",“args”:["/settings/admin/security"]},{“file”:"/var/www/owncloud/index.php",“line”:37,“function”:“handleRequest”,“class”:“OC”,“type”:"::",“args”:}],“File”:"/var/www/owncloud/lib/public/AppFramework/Db/Entity.php",“Line”:122,“CustomMessage”:"–"},“userAgent”:“Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.77 Safari/537.36”,“version”:“20.0.4.0”,“id”:“60b9fd4e8e306”}

I’m not sure but I think that the identifier in the oauth2_client table is the problem because the identifier, which is not a valid attribute, is located in this table.
I’ve already run maintenance:repair, db:add-missing-column, db:add-missing-indices and db:add-missing-primary-keys` but it didn’t help. Any idea how to solve this problem?

Operation system: Raspbian 10 (buster)
MySQL: 15.1
Apache: 2.4.38