Ringtones

Hi everybody. I have a problem. The ringtone (when someone is calling me) cuts off after approximately 2 seconds. Doesn’t matter which ringtone is set.

Have 15.1. iOS and iPhone 12 Pro. Does anybody know how to fix it or is it problem of current version of iOS?

I tried to restart my iPhone, change a ringtone, but nothing helped. When I go to settings sounds, the ringtone stops as well - immediately after the icon "silent mode off” disappears (it’s in Czech language). I am convinced, that this is just SW issue. But any suggestions, if something can help, what I can do myself?