Do You have on Your Machine more than one HDMI Plug so that You could try it on another one?
Do You run Your System with Xorg? You can check that in the Settings and there in the About Tab. Under the Hardware Stuff comes OS, Type and then Window Manager. There You have to look if there stands X11 or Wayland.
Then please change to Xorg and try it again. To do that, go to the Login Screen. there click on Your Profile so that the Password Field appears. It must be appeared! After it is appeared, You should see in the bottom right Corner a Gear Icon. Click on it. Then You should see 2 Options:
Zorin Desktop
Zorin Desktop on Xorg
Which Option is active, You can see at the Dot Marker at the Beginning. Choose the Xorg Option and log in. Then try Your Monitor.
I tried it, the xorg option before entering the password. It still isn't working. The HDMI port is functional cause the monitor detects connection but it says no signals.