I reinstalled Android, the SIM card still did not work properly. I was able to read the correct provider name in the phone settings. I tried different SIM cards from different operators, all had the same issue. I could read the operator correctly, but no cellular connection did not work.
Than GPS also started to show issues, in the first weeks I was able to get and hold a fix. But now the first fix was ok, but after a couple of minutes the GPS stopped working.
I opened the device, because previous owner said it got a new battery. half of the screw were missing. I needed my phone for work and had no time for further investigation.
In the end I bought a new Pixel 3a and am installing UT at the moment.