Follow-up:
reverting to the old installation (Rockstor 4.6.1-0 built on openSUSE Leap 15.4) worked fortunately.
To me it looks like Network Manager Wait Online is also failing, although rockstor in general does work without observable issues … 
admin@Kolibri:~> sudo systemctl status NetworkManager-wait-online.service
[sudo] password for root:
× NetworkManager-wait-online.service - Network Manager Wait Online
Loaded: loaded (/usr/lib/systemd/system/NetworkManager-wait-online.service; enabled; vendor preset: disabled)
Active: failed (Result: exit-code) since Fri 2024-09-20 17:35:03 CEST; 4min 6s ago
Docs: man:nm-online(1)
Main PID: 873 (code=exited, status=1/FAILURE)
Sep 20 17:34:33 Kolibri systemd[1]: Starting Network Manager Wait Online...
Sep 20 17:35:03 Kolibri systemd[1]: NetworkManager-wait-online.service: Main process exited, code=exited, status=1/FAILURE
Sep 20 17:35:03 Kolibri systemd[1]: NetworkManager-wait-online.service: Failed with result 'exit-code'.
Sep 20 17:35:03 Kolibri systemd[1]: Failed to start Network Manager Wait Online.
admin@Kolibri:~> sudo journalctl -xu NetworkManager-wait-online.service
Sep 20 17:34:33 Kolibri systemd[1]: Starting Network Manager Wait Online...
░░ Subject: A start job for unit NetworkManager-wait-online.service has begun execution
░░ Defined-By: systemd
░░ Support: https://lists.freedesktop.org/mailman/listinfo/systemd-devel
░░
░░ A start job for unit NetworkManager-wait-online.service has begun execution.
░░
░░ The job identifier is 245.
Sep 20 17:35:03 Kolibri systemd[1]: NetworkManager-wait-online.service: Main process exited, code=exited, status=1/FAILURE
░░ Subject: Unit process exited
░░ Defined-By: systemd
░░ Support: https://lists.freedesktop.org/mailman/listinfo/systemd-devel
░░
░░ An ExecStart= process belonging to unit NetworkManager-wait-online.service has exited.
░░
░░ The process' exit code is 'exited' and its exit status is 1.
Sep 20 17:35:03 Kolibri systemd[1]: NetworkManager-wait-online.service: Failed with result 'exit-code'.
░░ Subject: Unit failed
░░ Defined-By: systemd
░░ Support: https://lists.freedesktop.org/mailman/listinfo/systemd-devel
░░
░░ The unit NetworkManager-wait-online.service has entered the 'failed' state with result 'exit-code'.
Sep 20 17:35:03 Kolibri systemd[1]: Failed to start Network Manager Wait Online.
░░ Subject: A start job for unit NetworkManager-wait-online.service has failed
░░ Defined-By: systemd
░░ Support: https://lists.freedesktop.org/mailman/listinfo/systemd-devel
░░
░░ A start job for unit NetworkManager-wait-online.service has finished with a failure.
░░
░░ The job identifier is 245 and the job result is failed.
Cheers
Simon