Audacity & VAC: Error opening recording device (code -9999) in Windows 11. Problem solving
This short video shows how to fix that problem with Audacity record button error when Virtual Audio Cable (VAC) is installed: "Error opening recording device. Error code: -9999 Unanticipated host error".
Spoiler: in Windows 11 you have to enable microphone access (Settings - Privacy & Security - Microphone - Microphone access toggle ON).