Hi,

You should be able to install the NDI Tools pack from https://ndi.video/tools/ and run the tool called NDI Scan Converter. That will by default send the desktop of the Mac over NDI to be received by any capable receiver.

I would recommend to get a Zowiebox or Magewell Pro Convert that provide an HDMI loop through to capture the HDMI signal. Advantages are that you do not have to install anything on the Mac/PC and you get a nice, constant frame rate which helps when capturing video clips in presentations. You also get to capture audio which is not provided ny the Scan Converter.