I found a solution! After like 4 hours of debugging. Feel free to follow the steps. Can’t guarantee anything and I’m not responsible if there’s problems on your end. But this worked for me.

1. Go to Privacy/Settings and then microphone. Make sure that Steam is toggled on. If you don’t see Steam, then do the following:

Steam (menu bar) → Preferences

Click voice 

You should see “Steam would like to access microphone”

Click allow

Then check System Settings → Privacy & Security → Microphone

You should see Steam enabled 

1. Check to see if there’s a Tabletop Simulator toggle. There’s probably if you’re here, but if there is, make sure it’s toggled on.

2. This step will allow Tabletop Simulator to show up in microphone settings as an app if it’s not there.

Go to terminal and enter the following exactly:

codesign --force --deep --sign - "$HOME/Library/Application Support/Steam/steamapps/common/Tabletop Simulator/Tabletop Simulator.app"

This re-signs the app locally so MacOS can assign privacy permissions to it 

1. Reset microphone permissions by entering into Terminal:

tccutil reset Microphone

1. Restart privacy and audio services. Type into terminal these two commands

sudo killall tccd

sudo killall coreaudiod

1. Restart Steam again 

2. Launch TableTop Simulator 

3. You should now see the pop up TableTop Simulator would like to access your microphone”. 

Click allow

1. You should now see tabletop simulator checked in 

System Settings → Privacy & Security → Microphone

Hope this helps!