You aren't going to avoid a requirement to have either an iOS or Google Mobile Services Android device by using a non-AOSP-based Linux distribution. How would throwing away a whole lot more compatibility with apps/services avoid that requirement? It won't.
GrapheneOS is a mobile Linux distribution. Linux doesn't mean using glibc, systemd and GNOME. Moving to drastically less private and secure desktop software wouldn't be progress. That's the opposite direction from GrapheneOS.