How do I make my iPhone 12 Pro Max ring on incoming calls after updating to iOS 26.1?

First force restart it Force restart iPhone - Apple Support

Then, assuming that the calls can be answered but they are silent, exploring different stock ringtones, on full volume, both set in Sounds & Haptics.

Please ensure the physical ringer switch on the left side of the device is not showing the “orange bar” and is indeed set to loud for the ringer switch.