I use AIMP. My Library has roughly 6k files, it has replay gain and mostly when I add new files it notices it automatically and includes them in the library relatively quickly. You can also choose to manually scan for just tag or cover changes. And as a nice bonus, there are a few user made themes you can use to customize the look of the app. My only critique of the app up to date is, that the audio suffers a bit when using volume boost and that the ui requires a bit of learning how to use it.

thanks but i’d rather not have russian proprietary software on my phone

I also felt that way first but ultimately resigned as I couldnt find a decent alternative. Just curious, are you concerned about spyware/potentially malicious updates or do you just want to be sure/free of proprietary software?