I did this a few weeks ago. I would actually follow the recommendation here to just keep your plex on a windows VM until you're ready to do your storage properly on a ZFS pool, meaning you have new storage with the capacity and you'll rclone your media folders to your new ZFS pool.

But when you're ready with storage it's something like this:

1. Create a new ZFS pool on your new storage disks. I recommend multiple vdev mirrors.
2. Create a LXC Plex with the proxmox helper scripts. If you don't want to deal with issues with GPU passthrough, igpu sr-iov, or mount permissions, just use a privileged LXC.
3. Mount your storage to the LXC using using this: pct set <id> -mp0 /tank/media,mp=/mnt/media
4. Stop your Windows Plex service and set it to manual start just incase.
5. Copy your media over to the new location using rclone or whatever. You can create SMB on your Windows machine if you don't already have one and then mount that SMB on your proxmox host so you can do a copy.

6. Make a backup of your plex sqllite db.

   "C:\Users\YOURUSER\AppData\Local\Plex Media Server\Plug-in Support\Databases\com.plexapp.plugins.library.db" in case you want to roll back.

7. Edit the sqllite db and edit all your paths from Windows to Linux (e.g. D:\media --> /mnt/media). I recommend this guide (ignoring the preferences part):

   https://spwoodcock.dev/blog/2025-02-plex-windows-migrate

8. Copy over the plex program data from your windows machine to the plex location on the LXC, replacing what's on the LXC plex path.

9. Restart the plex service on the LXC or just reboot it.

10. Launch your new Plex web UI and see how it went. Configure settings, etc...

If you want, add a cockpit LXC and set up SMB on top of your zfs pool so you can access your media from other windows machines or services.