I buy most of my stuff via Bandcamp or Amazon Music. They're just mp3s and I use foobar2000 to listen/manage them on the computer, but in the past I also used MusicBee and it's just as good. I don't really have any good recommendations for mobile apps, because I listen to my stuff on an old iPod classic that I refurbished a few years ago.
Power Metal
Here be dragons. Dedicated to power metal and adjacent genres. Songs, albums, discussion, news, and memes, all is welcome here.
While linking to songs, try to use links that work in multiple regions (e.g. prefer standard YouTube links, not ("- topic" channels). Alternatively, provide additional links in the post body.
I listen through Tidal, but buy from Bandcamp. Bandcamp have an Android app that lets you play your music from them, either via streaming or offline. It's not great but does the job. I also use Shuttle+ on my phone. On PC I use MusicBee.
I usually just listen through Spotify, but for the albums I have bought physically, I usually rip them into FLAC files using fre:ac. Once I have the files, I place them in a cloud synced folder for backup, and in the Music folder on my desktop. I then use Clementine to play them, which gives a nice GUI from the metadata of the FLAC files. I also have a copy of all the albums on my phone, which I usually listen to through either VLC or "USB Audio Player Pro" (which, despite the name, is actually a good app).