I think you're looking for https://github.com/arabcoders/watchstate Watchstate will pull from Plex and migrate it into a Jellyfin instance. Emby is also supported. Works with multiple users as well, just do yourself a favor and make sure all usernames match up!!!
i've talked waaay to much shit to anybody who listen about windows to ever be seen using it again, i'm gonna have to install in the dead of night when everybody is sleeping, black ops type shit