As stated several times before, I am convinced this is a carrier issue that will be fixed via a iOS/carrier firmware update similarly to the issues experienced with the XS launch. I go days without any issues and then suddenly calls do not come through, but go directly to voicemail. If people hang up, I don't even know they called as no "missed call" is getting logged. I advised folks to leave a VM or text me in this situation. That is why I know it happens.
Verizon continues to fool around with tower set-up. Further, I believe the national 5G roll-out was rushed and causes issues as well. They won't acknowledge that publicly for sure. As stated in the thread by me and others, try out a t-mobile SIM to exclude a hardware issue. If you are within the return window, return your phone and wait it out. If you cannot return the phone and cannot / don't want to switch carriers, you will have to sit tight and hope for the best.