Hi, I had the mic error "may not be plugged in or is being used exclusively" for a while and I tried reinstalling software, drivers and restarting but nothing seamed to work. I did a bit of research and found something.
I use a usb interface (Audiobox USB) to connect my mic to my computer, and I started getting this error after I had moved my setup after moving house. The thing that fixed the issue for me was that you have to ensure that you reconnect your mic usb to the same usb port that it was originally connected with.
The reason is (and I'm not to savy about this so excuse the brief explanation) your computer designates an address to your mic when it is first installed, and this address is connected to the usb port witch you use the first time you set up your mic. Whenever you chose to use your mic, the computer checks the address to see whether the device is connected or not, so even though you may have your mic plugged in, if it is not connected to the original usb port or "address" it will not recognise it as connected, and assume it is not plugged in.
With a bit of trial and error (using each usb port one by one and restarting obs each time) I was able to find the right usb port and obs recognised the mic as it did before.
I hope this helps as this problem can be infuriating, though if it doesn't I'm afraid I cant suggest anything else.