So the question now is, how do I update it? In setting, it says there is an update and then it says: install manually please. And it's a clickable link. If I click on that, my browser downloads this file: PlexMediaServer-1.13.8.5395-10d48da0d-arm7.spk
I found this link where is a list of commands for updating manually through SSH. Will give it a go and see if it worked.
Upgrade Plex Media Server with PlexPass on LibreElec via Command Line | naschenweng.info