I don't suppose there's any firmware or whatnot that would turn an old Android phone (Pixel) into a dedicated media player?

I don't mean an Android app, I mean something like Rockbox that would just make it a wholly dedicated music player.

@jzb It should be possible: you can run Linux on many Android phones, and then there are music players for Linux. Or, it looks like you can compile Rockbox to run on Linux.

I think it's not trivial, but this could be your next hobby.