And that actually works, with an encouraging log file!
Back to my own mistakes: turns out I did not alter the PATH_TO_CONFIGURATION_FOLDER
to the actual desired path in /etc/systemd/system/habapp.service
(habapp) oh-user@server:/var/log/openhab $ sudo systemctl status habapp
● habapp.service - HABApp
Loaded: loaded (/etc/systemd/system/habapp.service; enabled; vendor preset: enabled)
Active: active (running) since Mon 2021-12-13 15:19:58 CET; 6s ago
Docs: https://habapp.readthedocs.io
Main PID: 25831 (habapp)
Tasks: 7 (limit: 2178)
CGroup: /system.slice/habapp.service
└─25831 /opt/habapp/bin/python3 /opt/habapp/bin/habapp -c /etc/openhab/habapp
Dec 13 15:19:58 Jedha systemd[1]: Started HABApp.
Now for me one question remains, and that is why the manual install did work and not the automated option 2B in openhabian-config? Was is updating python3 pip? Installing pendulum before habapp?
Guess there’s only one way to find out: deinstall HABapp on the other box, update pip3 and then do an automated openhabian-config install and see what happens.
Thank you Sebastian!