Symfonium is ridiculously customizable and well worth the one time cost IMO, but like you said it requires purchase and through the Play store.
DSub is on Fdroid and works well though it lacks many of the customization options that Symfonium has. It's kind of like a mobile mode of the default Navidrome webUI.
Those are the two I keep installed at all times because I use them for different things. The other options for Android either had weird quirks I didn't like or didn't offer functionality I needed.