I have iPhone 12 Pro but it’s not showing up ios 16 update. It’s showing me 15.7 as the latest software update
iPhone 12 Pro, iOS 15
After iOS 15.7 is installed, go again to Settings -> General -> Software Update.
Scroll down to -> Also available -> tap Update to iOS 16.
Additional:
Optimize the range of the mobile network, see this Apple article:
If you see No Service or Searching on your iPhone or iPad
If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support