Mac is recognizing monitor connected via HDMI cable even though the monitor is powered off

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Hi, I’m having an issue where a monitor is being detected by my Mac even though the monitor is not powered on, can you please help?

I have two monitors that are connected to my Mac via HDMI, but the monitors are both powered off (and the surge protector that the monitors are connected to is also powered off).

I want to make it so that these monitors will not show up in my display arrangement settings (or be detected as a display connected to the mac) when the monitors (and the surge protector that they are plugged into) are powered off. For some reason, however, these monitors are continuing to show up in my display arrangement settings and be accessible as a display on my Mac even though the monitor is completely powered off and the display is black. This is not ideal because I’m not able to use these monitors or see anything on them on the monitor when it is powered off, but the Mac ‘thinks’ that the monitor is still powered on so it makes it easy to lose windows or my mouse on these monitors.

When I disconnect the HDMI cable from the monitor(s), it disconnects the display in the Mac settings and completely fixes the problem; but I would much prefer to not have to manually disconnect the HDMI cable from the monitors to fix the problem. I also tested this with Displayport cables and Displayport cables don’t have this problem, but unfortunately my monitors don’t have any DisplayPort ports.

I’m imagining that the issue might be that the HDMI cables are ‘active’ or somehow transferring a bit of power to the displays from the Mac to make the Mac think that the monitors are powered on even though their not, but I am not sure. Does anyone know why this is happening?

Is there any way to make the Mac stop recognizing a monitor when the monitor is fully powered off (without having to manually remove the HDMI cable)?

Is there anything that I can change in the Mac software to fix this?

Or is there any hardware that would fix this? I was wondering if there are any passive HDMI cables, a displayport to HDMI adapter, or an HDMI splitter that might fix the issue, though a software fix seems like it would be least expensive if possible.

Thanks!

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What kind of Mac are we talking about here? What sort of connection are you using on the Mac end of these cables? (AFAIK the only Macs with 2 HDMI ports are some Mac Pro configurations with low end graphics cards) What sort of dongles are involved, if any?

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This is a 2019 Mac Pro. There are no dongles or adapters being used, just HDMI cables going from the Mac to the monitors.

The Mac has the least expensive stock graphics card (I think it’s a Radeon 570) as well as an AMD Radeon 5700 XT graphics card that was manually installed in a PCIE slot. I tried plugging in the HDMI cables to HDMI ports on both of these graphics cards but have had the same result for each.

I also am using Mac OS Catalina 10.15.7 if that matters.

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Thank you.

I’m not familiar with many of the HDMI terms that you mentioned (including HDMI Matrix, EDID and CEC).

I just tested using a cheap Techole HDMI splitter that I had laying around (https://www.amazon.com/gp/product/B079JQ9XXV/ref=ppx_od_dt_b_asin_title_s01?ie=UTF8&psc=1) and it did not help to fix the problem.

I tried searching Amazon and google for "Metra Home Theater HDMI matrix splitter” and "Metra Home Theater HDMI matrix splitter” and found the two following results, but I am not exactly sure what I’m looking at and both of these are out of my budget price range:

I would prefer to fix this problem for free or under $50 if possible.

Can you please advise on whether the links that I found are what you were describing or, if not, provide links to what you were describing?

Also, do you think that there is any other less expensive way to fix this? Fixing it with software on the Mac would be great, or I imagine that I might be able to use a different kind of cable or a $10 HDMI to DisplayPort adapter since the issue does not happen with DisplayPort cables.