Graphene is all fine and well but only has builds for a handful of models from a single manufacturer and the oldest model that they recommend using was released just 13 months ago, suggesting users will need to buy a new phone on a very regular basis.
It's not really relevant to this guide's "User and device requirement":
> ANY Android 9+ device (Android 10+ recommended for better security)
Graphene is legit. I've used it for a while now and have no complaints except being unable to cast to a Chromecast (yes yes, I know), but I have an old Android phone for that.