My Note 10+ call volume became super low last night after using the USB-C headphones. Now when I answer calls without the headphones, I have to strain to hear the other party via the earpiece (at full volume)... the issue extends to speaker phone mode as well.

I've tried plugging in the headphones, using them for a call, removing them. Also tried restarting. Tried being in call and reducing the volume to low and putting back up to max. Still the same. Almost sounds like the earpiece wire is loose (like when your car speaker has one wire a bit loose)... but then that shouldn't affect speaker phone mode since the audio comes out of both speakers on the phone.

Going to try restore to factory now.

Yes. Updated, rebooted, factory reset. USB-C headset works perfectly, BT headset(s) work perfectly.

Speakers I think are actually working fine - because the if I had broken the speakers by playing something too loud (no I didn't), the volume would be unaffected but I would have crappy sound. Instead, volume is super low on both speakers, and the audio is just crackly and sounds like the equalizer got adjusted to over 9000. Most of the time, I'm on headphones (USB-C or BT) so unlikely I would have blown out the speakers... and I'm an uncle anyway so I don't blast anything on my phone.

I'll drop by Samsung on Saturday and see if they can perform some magic and get me a replacement within the same day (they magically managed this with my Note 9 motherboard issue). I'm starting to see a pattern here...