I upgraded my Ubuntu server to 22.04.1 and reinstalled plex, now Plex cannot find any of my files

You misunderstood.

The design and implementation of Gnome desktop forever prohibits another user (plex) from seeing any of your files in /media.

Notice the naming: /media/YOUR_USERNAME/volume_name

You must move the mount point (manually create one) away from /media/YOUR_USERNAME using a manual mount

-OR-

Change PMS to run as your username.

There is no choice in this. One or the other. Linux is strict about preserving permissions and privacy between different usernames (you vs plex)

You can customize Plex to run as your username but that’s a bigger task.

Here’s the How-To to make your media visible to plex

Here’s the How-To to customize PMS to run as your username