I finally found the add-on causing the issue, turns out is actually the last add-on I installed: Grid fields from @abdo (not the one from ankiweb)
Abdo, if its not too time-consuming, could you check it out? When the backup triggers Anki freezes. That happens when the browser window is open (and I guess the add-on is active as it only works on the browser window). Having the browser window open for long increases the likehood of triggering the issue. I usually check ChagtGPT to explain sentences and then generate some images so this process is a good way to try reproducing it.
All Anki 23.X versions I used had this issue. Not 100% of the times, but most of the time. Enough to kill Anki process several times per hour.