abbluiz I have 2 Pixel 7s with Graphenos and one Pixel 7 has the same problem with freezing after an update pops up in the Google Play Store and I installed it too quickly by clicking without reading. The problems started there. Every time I opened a contact in my Signal Messenger to write to them, I had a banner saying that the signal wasn't working properly and they wanted a diagnostic report to analyze it. I was only able to free myself from freeze by holding the Shut Down button for at least 12-13 seconds and opening a window for half a second (which looked different than the standard graphenos shutdown layout) where the "Restart" button could be seen. I had to click on this with a quick reflex, otherwise I would be back in front of the freeze screen where nothing worked.
Only a completely new graphenos flash helped and fixed this phänomen. I also recommend switching to the Pixel 8, as you can activate memory tagging only on the 8 series for more hardening memory security (see matchboxbananasyngie's post "MTE support status for GrapheneOS")
That's why I'm going to buy a Pixel 8 tomorrow, remove all sensors and then flash it to activate MTE support for even tougher security.
Otherwise you can re-flash once, it solved the problems for me.