I've installed the 24.04-1.3 RC 1 release on my Fairphone4 today.
I was able to call through 4G network with VoLTE and I received one too. I was able to send a SMS too.
I was able to open the Signal UT application from the OpenStore correctly (it uses X11).
I think I'm not able to test the other items.
I noticed one regression: in the top bar, the cellular network indicator (the triangle on the right of Bluetooth icon) is always empty. It does not report the signal strength. Fortunately calls/SMS work like I reported above.
Thansk for this RC 