I had same issue. And I was facing every few hours. Then recalled when it happend last time. I was on a whatsapp call and I received Google Duo call which I had disconnected. Since then it was happening. For you it may be other case.
But then I forced stop Google Duo and it worked. If its happening to you, try to recall and disable apps which can be causing this.
Yes my volume is not working as well on my Note 10 plus I can be in my car listening to my music and the sound will decrease on its own, I've even used an auxiliary cord and it's still decreases and if you have your phone on do not disturb mode you cannot hear any volume until you take your phone off Do not Disturb mode it bothers me because I spent so much money on this phone. They need to get this together why would I or anyone else purchase a phone that's over $1,000 and they don't have their s*** together!
If something is broke you normally take it back I know they wouldn't like it if all of their consumers requested a refund
Im having the same kind of problem with playing videos with lowest volume and have to restart the phone to fix it and i notice it happens when I receive the call and after the call ends if I play video from galery it plays with lowest volume which I can not raise the volume and everytime I have to restart the phone. Sometime I try to play a video and it says can not play the video during the call and at that time I'm not even on the call and only fix is to restart the phone, don't knkw how to fix this problem permanently as I'm really getting sick if these problems
Same issue with my Galaxy Note 10+. The problem occurred a few months before and it was fixed automatically I don't know how. But from the last 2-3 days, the same problem has started to appear once again. And now the other problem is after some video calls or online classes, the external sound from the device comes from the earpiece only which is disgusting. I have to always restart my phone to get back it to normal.