After fiddling around a bit, found somewhat of a fix for the error at least. A few days a go i added 2 Fields to this window, so i can automatically generate furigana for my cards when i add them.
Screenshot 2022-08-07 184108.png
After removing them, the Error disappeared, but obviously also the automated furigana generation. I can live with, for now, manually generating it, but if this has been a hint to figuring out the issue, i would appreciate any help.