Clips does not currently support capturing internal system audio (such as sounds from other videos or applications) during screen recording. The only way this audio is recorded is if it’s picked up by the microphone or routed through a virtual audio device configured as the input source.

I’d like to request native support for capturing internal system audio directly within Clips, without requiring my speaker, or the use of a virtual audio device or third-party tools to route system sound through the microphone input.