No HDMI sound through Mac Mini M4 Pro

I've been trying to connect my Sony RF Wireless Surround Headphones (TML-L600) to the Mac Mini HDMI port unsuccessfully.

The headphone base unit connects via HDMI cable, and appears as a surround sound amplifier to the source component. I've used these extensively with my Denon AVR 6700 for late night viewing. After reading the blogs and Apple help articles, I can't get my M4 mini pro HDMI port to show up on either the Sound Setting or the Audio Midi Setup utility.

Can someone advise as to how to activate the HDMI port?