Ignore this section of the settings. It is only pertaining to the old Python-based agents, which are deprecated.
You are using the new agent “Plex Music”. All settings related to this agent can be found directly in the properties of the library, on the “Advanced” tab.
I think Plex Music is also using fanart (among others). So you should be able to select it when editing albums and/or artists in Plex.
Never downgrade the agent from Plex Music to one of the older ones. It can mess up your library beyond repair and you’ll have to delete and recreate the whole library.
If you care much about proper artist and album art, you should acquire it as separate jpg or png files in high resolution. Then place these files directly beside your music.
Naming convention can be found here: [BUG] Plex isn't picking up artist images (folder.jpg) - #2 by OttoKerner
That way they are backed up together with the media (you do backups, don’t you?) and can be picked up automatically if you ever have to recreate the library for some reason.
