I have been running Graphene on a Pixel for a while now and I don't think Linux phones are a viable alternative. The vast majority of Android apps just work on Graphene, and there are millions of them. The UI experience is polished, everything just works with the exception of apps that require Google Play Integrity. And of course these projects aren't affected by Google's restrictions on sideloading.
Look I love that GrapheneOS exists, and I have used it in the past (as have I with Lineage).
But GrapheneOS lives by the mercy of Google. Pixel devices being reference devices makes it so that it's unlikely that Google will close them down completely.
However, as can be seen with this verification move, Google is willing to go very far to accomplish its aims. They already delayed delivery of Android 16 images, causing GrapheneOS some headaches.
Waydroid exists and a mobile distro that provided Waydroid OOTB would be as usable as a full-on Android phone. You could even build it to remove the app verification stuff if that found its way into AOSP.
Just wished there was a viable* FOSS Linux based mobile OS project out there that I could offer my time and energy to instead.