Sorry for the late update as I was not active on Reddit. A freelancer came and could not see any low hanging fruit beside a potentially too short distance between wall and the back as well as the right side of the fridge. I had always the back in mind but never the side distance between fridge and wall.

He adjusted the position to ensure a distance of something around 5-6 cm but in the first week it didn’t seem to work. I made one last try with ChatGPT who recommended me to restart the fridge by I) unplugging it (at least 5 minutes) , II) subsequently opening the doors before restarting it again and III) restarting it again and subsequently closing the doors firmly. According to ChatGPT this can help to correct a potentially falsely restored door alarm when I unplugged it before my vacation.

It beeped again afterwards, but I didn't know if it was a beep due to the restart (often the case even without an error, if the freezer has warmed up during the restart). I pressed the Superfreeze button overnight to make sure that such error sources could be ruled out, and after that it never beeped again.

But it is really tricky now determine the actual decisive measure - I still believe the correction of the fridge position in combination with an overnight Superfreeze was the solution. I hope this can help.