Can't access Home Assistant GUI (supervised, debian 11) anymore

I set up Home Assistant Supervised some months ago on a Intel NUC with Debian 11 according this guide (Installing Home Assistant Supervised on Debian 11).
It worked fine until a power failure last week. Now I’m not able to open the GUI anymore - I can’t imagine what caused the problem. ha commands don’t work anymore.

As I tried to update the whole system I got following error message:

dpkg: Fehler beim Bearbeiten des Paketes homeassistant-supervised (–install):
»installiertes post-installation-Skript des Paketes homeassistant-supervised«-Unterprozess gab den Fehlerwert 1 zurück
Fehler traten auf beim Bearbeiten von:

Is there any possibility to repair the system?