Thanks to @antonok libcall-ui's main branch now uses GTK4/libadwaita. We've also tagged 0.2.0~beta1 for that.
For GTK3/libhandy applications there's still the 0.1.x branch.
@agx For context, libcall-ui is a dependency shared by the Calls app and Phosh itself.
GTK4 Calls and GTK4 Phosh coming soon* to a #mobilelinux phone near you
*pending a little more porting