Thank you for your answers!
I tried rebooting into safe mode and everything works normally. The issue I have now is figuring out what is causing the problem
I haven't installed anything new in between the two Calibre versions. I tried deactivating most of the programs that start at boot and turning off realtime protection on Windows Defender but no luck there either. Tried also Calibre in debug mode but even though I open the editor nothing weird shows up in the log (at least not that I can see).