If you are having trouble with your voice chat, here's some things to try.
This bug can happen after an update, clearing out OS level permissions to access the microphone. In this scenario, your mic is working fine in other games and applications, just not Killer Queen Black.
Here's a step by step guide to resolving this issue. Not for the faint of heart! Proceed with caution.
Disable System Integrity Check (Reboot Into Recovery Mode)
Reboot back into normal mode.
Perform Terminal Incantations
sudo sqlite3 ~/Library/Application\ Support/com.apple.TCC/TCC.db "INSERT or REPLACE INTO access VALUES('kTCCServiceMicrophone','com.Company.ProductName',0,1,1,NULL,NULL,NULL,'UNUSED',NULL,0,1551892126);"
/usr/libexec/PlistBuddy -c "Add NSMicrophoneUsageDescription string" ~/Library/Application\ Support/Steam/SteamApps/common/Killer\ Queen\ Black/Killer\ Queen\ Black.app/Contents/Info.plist
/usr/libexec/PlistBuddy -c "Set :NSMicrophoneUsageDescription Using voice chat" ~/Library/Application\ Support/Steam/SteamApps/common/Killer\ Queen\ Black/Killer\ Queen\ Black.app/Contents/Info.plist
Re-enable System Integrity Check (Reboot Into Recovery Mode)
Reboot back into normal OS mode.
You should now be all set!