A MacBook is preset to automatically enter sleep mode when inactive. In this state, the Jabber client no longer works and incoming calls are not signaled. The following steps are necessary to prevent this.
The current Jabber client still has a problem on MacBooks with M1 processors. Connected headsets on the MacBook do not work or the voice transmission is heavily disturbed. To work around this, the Jabber client has to be started with the macOS option "Rosetta".
Find out if the MacBook has an Apple M1 processor:
https://support.apple.com/de-de/HT211814