The most basic level is GitHub, Gitlab, etc are used to store version controlled files which can be anything from like a wiki, an apps source files, your random collection of scripts, etc.

They have added features like the ability to offer artifacts which could be an already compiled exe or rpm, or just the source code for you to self compile. Which option they give is dependent on which repo and usually that repo maintainer will have directions for how you install their thing.

There is on the main list of artists but I would test it first on a single artist/album

Couldn’t you just fix the naming settings to include the album and then pick an artist and preview rename and see if it fixes it will fix it?

Lidarr is centered around full albums unless a song was released as a single, specifically it uses release-group on musicbrainz.

I run both jellyfin and Plex, and for the music app I think plexamp > finamp, but both work to sync between their respective instance. I haven’t tried anything else because I already had Plex pass for other things.