The snap does not include driver support for GPU’s and it isolates Plex from the one’s you installed.
Be aware that the Plex install/data directory is or use to be different /var/snap/plexmediaserver/common/Library/Application Support vs /var/lib/plexmediaserver.
If it is and you want to transfer your current data you will have to cp or move it to the new location, don’t forget to check file ownership afterward, should be plex.
