Are you sure? You’re the first to report it in that case 
When did you get that update?
For info, updates for the FP3 are registered in this topic but sometimes unofficial releases get out into the wild … could even be the reason behind your VoLTE problem as the carrier is likely unaware of it.
Yes, Android 13 is currently being tested and is expected to reach all users in June according to an official communiqué. It might be worth waiting for that.
Don’t feel you’re a nuisance, we’re all interested in how things work or why they don’t 