it works when i execute it on the client. removed the cache and it still works.
after i did cmk --debug -vvn serverxyz.domain.de again, i can see this (because i enforce the apt-service for testing purposes):
APT Updates PEND - Check plugin received no monitoring data
CPU load 15 min load: 0.04, 15 min load per core: 0.02 (2 cores)
Check_MK Agent Version: 2.1.0p9, OS: linux, Agent plugins: 1, Local checks: 0
Filesystem / 27.78% used (16.06 of 57.79 GB), trend: +77.61 kB / 24 hours
Interface ens160 [2], (up), MAC: [...], Speed: 10 GBit/s, In: 14.7 kB/s (<0.01%), Out: 3.80 kB/s (<0.01%)
Memory Total virtual memory: 47.2% - 1.37 GB of 2.90 GB, 9 additional details available
Uptime Up since Jan 02 2023 14:14:28, Uptime: 1 day 0 hours
The PEND won’t resolve in OK or WARN.