Thank you for your reply!
I got this part working now (it took a restart of REW for me I think).
But I'm not trusting the SPL readings. They seem low (or I'm measuring an unusually bad driver). Is there any possibility the latest Windows 11 settings have changed in a way that can affect SPL...
EDIT:
Somehow it works now. I can change the volume of the microphone under windows settings and REW picks this up and adjusts SPL accordingly.
However.. I don't trust these SPL readings at all. They seem a bit low. (no way to check any other way right now)
Are they trustworthy this way or is...