System Volume doesn’t lower itself while on FaceTime Call

Hello,

so you all probably know, that your system volume should automatically lower itself while on FaceTime or a normal Call.

Well it doesn’t do that anymore since I got my new Phone, on my 13 it was fine but since I have the 15 pro max I can’t do anything anymore while in a Call because everything is just too loud and I can’t understand the person on the end of the line. Is there an issue with the phone? I can’t find any setting or similar posts to this problem.