I use a simple custom DB [0]. my DB is my library: Lists of artists and albums, enriched (and updated) with data from APIs (last.fm, RYM, spotify) for filtering, organizing....
I have learned not to invest anymore time in organizing files (structure...) and files metadata (correction....). I just leave it as it is. it is not "pretty". But my UI is my DB so who cares. I just do a simple folder search [1] or take out that vinyl, when I need to.
I store all my digital playlists in the same text files: M3U, Spotify URIs, YouTube URLs, it does not matter. I guess you could call it an agnostic system.
It works for desktop. Mobile is trickier.