I am not asking where did you download openplotter-settings from, I am asking what version is your Debian system.
I think you forced the installation of openplotter-settings v3 (for debian bullseye only) into a system running openplotter v2 (for debian buster only).
Downgrading after an update is really weird and that's the kind of paranormal effect of a broken debian. I can only advise you to start from scratch with the official image of openplotter v3: https://cloud.openmarine.net/s/mxrBi5K7zRj2gDq
I think you forced the installation of openplotter-settings v3 (for debian bullseye only) into a system running openplotter v2 (for debian buster only).
Downgrading after an update is really weird and that's the kind of paranormal effect of a broken debian. I can only advise you to start from scratch with the official image of openplotter v3: https://cloud.openmarine.net/s/mxrBi5K7zRj2gDq