I had the same question a few years ago. This is how it was explained to me;
…Roon software lists all HDMI ports which includes Display Ports (and maybe even DVI ports?) that are either available on the motherboard video chipset, or the processor chipset in the case of Intel processor integrated video, even if all ports aren’t physically installed in the motherboard backplate, so this is somewhat common…
My streamer/core (Salkstream III) only has one HDMI connection. This is what I see in Roon. In my case, HDMI 2 (labeled Oppo 103 in the pic) turned out to be the one for the HDMI connection on the Salkstream.
