As per the werk Platform update to Debian bookworm , the Checkmk versions have to be re-installed.
The update from firmware 1.6 to 1.7 is a major platform update. In this step we move the underlying OS from Debian buster, which reached it's end of regular support EOL in 2023-09 and will reach it's LTS EOL in 2024-06, to Debian bookworm.