... Ok so it looks like the right hdmi port (when looking from front of box) has an issue booting on a monitor, could be an audio thing. When I booted with left HDMI it worked.
I had a similar problem with RPi4. Plugged into right HDMI and no audio. Spent a while (too long) checking settings. Then plugged into left HDMI and everything was fine. I was happy that it worked and haven't looked any deeper since.