Download the shit I want, stick it on a USB key and plug it into my car. The old magics.
If you're talking about ambient music then you have things like Navidrome or Jellyfin that can stream music throughout your house.
Ad hoc, on device streaming: I use PipePipe, choose a YT music playlist and just...play in radio mode. There are better options (like InnerTune) but those tend to crap out when YT futzes with their back end / aren't updated as frequently as PipePipe.
I also have an iRiver MP3 player (about size of a box of matches) that's awesome.
Don't let the perfect be the enemy of the good.
