It's really easy. Graphene has a web flasher with very good instructions, and once flashed, you're good to go. I haven't looked back. Once installed you'll want your apps.
If you want to sign in to the play store and connect your google account to the phone for your apps, you can do that, bu then you're kinda right back where you started. Not fully, because Graphene, but Google is still gonna google and suck up any and all data it can.
So for apps, look to F-Droid, Obtainium, and Aurora store.
F-Droid and Obtainium for FOSS apps, and Aurora store for play store apps without having to sign in to the play store.
Looks like I'm an outlier here. I run navidrome on my server, but for jams on the go I use a HiFi Walker H2 dac/mp3 player with Rockbox. I sync my library from the server to the sd card when I add new music/podcasts/audiobooks. I wrote a python cli tool for the syncing.
At home I use the web interface on my laptop, and an old android (wifi only) phone connected to Bluetooth speakers for kitchen tunes.