I am trying to do the same migration from plex to jellyfin but jellyfin keeps crashing on the server with ‘out of memory’ in the logs. As soon as I can stabilize that I will dump Plex lifetime. I initially had sync server setting turned on in Plex and Plex kept sending cleartext phone SMS about what I had watched the day before. That is turned off now. I asked Plex corp for a copy of my data. They sent it to me but ‘forgot’ to send the database table with watch history. They sent me that table when I complained it was missing. Fuck Plex and their spyware.