I think I have figured this out... I made an account just to post a reply to maybe help others. I am using OBS and the virtualcam plugin to bring video into Microsoft teams. I wanted to use the OBS audio output as a input for microsoft teams so that I could take advantage of filters that I have on the mic in OBS rather than running the Mic directly into Teams. Here is what worked for me.
Step 1: In OBS in the Audio Mixer panel at the bottom, click the settings icon next to your microphone, go to Advanced Audio Properties, and turn on Monitoring for your microphone. I have it set to "Monitor and Output" because I like to use the record function of OBS to test things, if you select "Monitor Only" the mic will not work with the record or stream functions of OBS but can still be used in other applications.
Step 2: Find and download a Virtual Audio Cable program (google). I'm using the VB-Audio Virtual Audio Device. Follow the instructions to install, in the cast of VB-Audio application I downloaded, unzipped, and ran the .exe setup file.
Step 3: In OBS at the top of the screen, go to File -> Settings -> Audio (tab). Under the Advanced panel look for "Monitoring Device". Set this to the input for the virtual cable application "Cable Input (VB-Audio Virtual Cable)" in my case. If you do not see this you may need to close and reopen OBS, restart your computer, or double check your install of the Virtual Audio Cable application.
Step 4: Open the application that you want to use with OBS audio. In my case Microsoft teams. Change the microphone input device to the output of your virtual audio cable application, in my case ""Cable Output (VB-Audio Virtual Cable)". Again if this doesn't appear, try restarting the application or your PC.
Step 5: That's it, it worked for me, I hope it works for others too.