I had these issues with my first Pixel 8 Pro that I had GrapheneOS on last year. It was infuriorating and I thought I had tried everything. In the end, it turns out it was a hardware issue - corrupted memory I believe. So, I returned the phone, got a Pixel 9 Pro and since then (a year now) have not had one issue.
The way I found the error was to save the error codes when things crashed, and then fed the output to my local LLM (Ollama, WebUI, Gemma 7b, offline, and not connected to the internet for privacy sake) which translated the reams of code to say it was a memory hardware issue. It's worth a try, at least to see what the diagnostic comes back as.
Hopefully that helps someone on this thread.