I hope your issue has been resolved by now. I too have a pixel 8 with no City Issues but out in the country is something else, which is besides the point of your issue. I noticed mine now reads 5G+ occasionally which is nice. How many bars did your old phone get?
1) Have you put it into Airplane mode and then off again?
2) ReStart is alwats a good idea.
3) Did thge SIM card go in easily or did you have to struggle?
Please keep your post up to date so we can track you solution.
Good luck.
Just a Google User
