I have similar issues, and posted about it in a separate thread.
Make a long story short, a good number of Pixel 7 users (including myself) have issues maintaining calls. There are conflicting ideas as to why this is the case, mostly to do with hardware issues. I went through network resets etc, and, as far a making and taking calls go, all I could do is disable VoLTE in the settings (Settings - Network & Internet - Internet - (Click the tar next to whatever network you're on) - scroll down to VoLTE nd toggle to disable it.
This way, you retain your LTE / 5G data connection, but your voice calls will be routed via the 3G network. You will lose some voice sound quality vs VoLTE, but you will maintain your calls properly. It is not an ideal solution, but at least you can use your phone as, well, a phone.
Hope this helps.
I forgot to mention that it is happening all over the place, be it Europe, North America etc. or network carrier.