I’ve recently had really good luck with Finamp on Android at least. With the recent support of time lyrics in Jellyfin and Finamp’s redesign I’ve been using that to stream my Flac audio files. Works quite well with separate collections as well. Though, to this day I still have to force close it more times than I like to get the UI to refresh after closing it. Plexamp was tough to lose when I swapped many years ago, but the third party space has slowly been closing that gap over the years.

Remember that this does not include the source engine which is still closed source, good for modding but you won’t be able to do crazy ports or anything anytime soon.