I have this problem too, and I just got the iPhone a month ago!!
There are two problems for me.
First one, there are two speakers on the iPhone 13, one is the earpiece speaker the other is the bottom speaker. The bottom speaker does not output any sound whatsoever, only the earpiece speaker does.
The second one, iPhone also gets really, really glitchy/non-responsive when I try to play anything with sound in it- Youtube videos, Photos videos, Spotify, even changing/testing the Ringers & Alerts volume makes the phone unresponsive for a moment.
I've tried hard resetting the iPhone and the problem still persists. PLSSSS HELP ITS A BRAND NEW PHONE (no external damage)!!