I definitely have this issue as well...and it's maddening. I'm on a desktop, wired speakers, everything set the way I want it, then Teams blasts out on calls which makes me jump almost every time. This is nuts, there should be a switch in Teams that says 'Do not change volume on anything, EVER'.
Tried just about every solution in this and other threads and still doesn't work right and blasts volume (so if I was listening to something and place a call the volume blows out). Tried volume mixing settings, Communication device settings, app volume, device settings, exclusive device access, etc. Nothing fixes this and it's unbelievable there's no fix for this after all the complaints.
This seems to be related to the new Teams client, didn't have this before. There needs to be a switch in Teams to stop this behavior (this problem only affects Teams, nothing else).
Microsoft--this isn't a volume level issue, a device driver, some deeply buried function, it's a BUG in Teams (or at least a feature you have no exposed UI for).