Thanks for lightning-fast replies! Yeah, that page doesn’t lead to anything else… Maybe it sends feedback to Fairphone, but nothing is communicated to me.
Good point about my SIM card. It’s 2 years and 3 months old, physical. VoLTE works on my previous Galaxy A22, but it caused problems in Fairphone 6. I got calls from “Unknown” without the ability to call back. When I disabled VoLTE, I could see the calling number and hear them, but the other party couldn’t hear me. I had to switch to using 3G for calls to work properly.