Had similar problems with my P6P. There are multiple areas in my town where I show full / nearly full bars, but my service is terrible or non-existent (!). If I toggle Airplane Mode, I’ll get great speeds until it drops out again. Sometimes this is 30 seconds, sometimes 30 minutes, sometimes hours/days. But at some point it will drop out again. Ugh…
I think the pixel 6 pro had a shitty 5g modem. I’m using one on a verizon mvno and it works fine but definitely has a shitty signal compared to my iPhone.