I can’t connect to my carrier

See this...Update your carrier settings on your iPhone or iPad - Apple Support

And/Or...If you see No Service or Searching on your iPhone or iPad - Apple Support

This may apply to your phone...iPhone 7 Repair Program for "No Service" Issues - Apple Support

Also...If you see an Update Failed or Apple Pay Not Available alert after iOS update or restart - Apple Support

call carrier - I had issue on new iPhone 11 pro and the carrier had to send signals to force my phone to accept the handshake

BUT it worked on wifi calling not cellular