Thanks for the hint.
Just removing the file didn´t work immediately, updating the “core configuration” failed again. This time i got this error log:
2024-07-12 08:27:57 - Updating site 'KFO' from version 2.2.0p30.cce to 2.2.0p30.cre...
* Updated etc/mk-livestatus/nagios.cfg
* Vanished var/check_mk/reports/archive
* Vanished var/check_mk/reports
* Vanished var/check_mk/rrd
* Vanished etc/logrotate.d/mknotifyd
* Vanished etc/logrotate.d/dcd
* Vanished etc/logrotate.d/liveproxyd
* Vanished etc/logrotate.d/cmc
* Vanished etc/ssl/saml2/builtin/signature
* Vanished etc/ssl/saml2/custom
* Vanished etc/ssl/saml2/builtin
* Vanished etc/ssl/saml2
* Vanished etc/rc.d/20-mknotifyd
* Vanished etc/rc.d/85-dcd
* Vanished etc/rc.d/80-cmc
* Vanished etc/rc.d/20-liveproxyd
* Vanished etc/cron.d/cmk_license_email_notification
* Vanished etc/init.d/mknotifyd
* Vanished etc/init.d/dcd
* Vanished etc/init.d/liveproxyd
* Vanished etc/init.d/cmc
* Vanished local/lib/python3/cmk/gui/plugins/reports
* Vanished local/lib/python3/cmk/cee/dcd/plugins/connectors
* Vanished local/lib/python3/cmk/cee/dcd/plugins
* Vanished local/lib/python3/cmk/cee/dcd
* Vanished local/lib/python3/cmk/cee
Creating temporary filesystem /omd/sites/KFO/tmp...OK
Executing update-pre-hooks script "01_mkp-disable-outdated"...OK
Executing update-pre-hooks script "02_cmk-update-config"...
-| ATTENTION
-| Some steps may take a long time depending on your installation.
-| Please be patient.
-|
-| Verifying Checkmk configuration...
-| 01/04 Rulesets...
-| 02/04 UI extensions...
-| 03/04 Agent based plugins...
-| 04/04 Deprecated .mk configuration of plugins...
-| Done (success)
-|
-| Updating Checkmk configuration...
-| 01/22 Update LDAP connection ids sync time files...
-| 02/22 Validate user IDs...
-| 03/22 Update views...
-| 04/22 Update dashboards...
-| 05/22 User attributes...
-| 06/22 Global settings...
-| 07/22 Update LDAP connection ids...
-| 08/22 Rulesets...
-| 09/22 Autochecks...
-| 10/22 Remove unused host attributes....
-| 11/22 Convert persisted sections...
-| 12/22 Cleanup version specific caches...
-| 13/22 Background jobs...
-| 14/22 Extract remote sites CAs...
-| 15/22 Add a rule_id to each notification rule...
-| 16/22 Change absolute paths in registered hosts symlinks to relative...
-| 17/22 Synchronize automationuser secrets...
-| 18/22 Remove old custom logos...
-| 19/22 Check for incompatible password hashes...
-| 20/22 Update backup config...
-| 21/22 Event Console: Rewrite active config...
-| 22/22 Sanitize audit log...
-| Done (success)
OK
Updating core configuration...
Configuration Error: No module named 'cmk.base.cee'
Could not update core configuration. Aborting.
I then tried to update the config manually by typing omd config sitename → basic → core → changing from cmc to nagios and this change just worked perfectly fine. So everything is working now