I also have the exact same issue on my MacBook Air M2, audio/video playback when using a USB-C to HDMI adapter is in fast forward when connected to an extended display wether it be via the cable or via dock which then utilises a HDMI to HDMI cable. I notice this is only when trying to use the sound from the external display. When using the MacBook speakers this issue does not arise. This is particularly annoying when you want to take benefit of your home theatre speaker setup to watch movies/tv shows etc. Hopefully this bug will be fixed soon as I have tried many different cables/docks, non seem to work.