At a minimum, eARC requires that both an audio device and its connected HDMI port support HDMI 2.1. If you're unsure, check your audio gear's specifications, and connect it to the port marked "eARC" ...
The Asus TUF Gaming B860M-Plus WiFi isn't especially gaming-focused, despite its name, but the overall feature set isn't too bad for the money. However, you can get better m-ATX Arrow Lake ...