I have a 2017 MacBookPro. When I connect my laptop to HDMI display, audio goes straight to HDMI. I can't control the volume. It is mildly annoying but I can understand there are some benefit in better sound quality.
What really bothers me is that I cannot mute/unmute the sound from my keyboard. Is there a way to let me control the HDMI audio from my laptop, at least mute/unmute?