Clicking Display Settings "USE HDR" kills 4K HDR LG C1 TV screen

I posted this question on Tom's Hardware, but it was suggested this forum might be helpful as I have a new problem with Windows 11. When I plug in my HDMI connection into the Strix SCAR 17 SE for my LG C1 tv, it sees the tv as a second display. I use WINDOWS +P to black out the laptop screen and use the tv at full resolution. It shows up at 3840x2160@60Hz. However if I go into Display Settings and try to set the tv to USE HDR, the tv screen wavers then disconnects and stops being recognized as a second display. And it reverts to my laptop monitor. I can't turn USE HDR off, because it says display not active... I have an XSX and PS5, as well as a 4K apple tv, and they all run fine in 4K HDR on this tv. I use Zeskit 8K HDMI cables for all the connections. The only way for me to recover the tv as a second screen is to reinstall Windows 11 and go from there... but don't click USE HDR.

As background, I was using my Asus G733QSA ROG Strix 17 without any of these connection problems at all. And I set the SECOND SCREEN to the 3840 tv resolution and HDR. Same cable. Same tv. No problems.

But I recently upgraded to the new Asus ROG STRIX SCAR 17 SE with Windows 11. The new laptop has a 2560x1440 resolution at 60/240Hz. The old laptop had a resolution of 1080p at 60Hz. My LG C1 operates at 3840 resolution of 60/120Hz with full 4K and HDR. When it's functioning as the non-HDR 4K second screen, it is broadcasting at 60Hz. The G733SQA operates at a 1080p resolution and 60Hz.

There isn't anything wrong with the HDMI port, as everything works fine initially because it will allow 4K to be broadcast, just not in HDR. However, I would love to use the HDR just like I did with my previous ROG Strix 17. The new laptop meets HDMI 2.1 spec.

Any suggestions? I am at a loss how to fix this problem. Tried reinstalling Windows 11, uninstalling graphics drivers, check for Windows Updates, unplugging/replugging HDMI at different points, etc. Nothing seems to work. But if I take the HDMI cable out and plug it into the old laptop... everything is normal. The old laptop sees the tv as a second screen and outputs 4K HDR.

Might be way off the mark here but, does the old laptop include a MUX switch and the new one doesn't?

Well, exactly the opposite. My old laptop didn't have a MUX switch, but the new one does. Can a MUX switch cause HDR output issues?

Well the purpose of a MUX is to allow a dedicated GPU in a laptop to bypass any splitting hardware and output directly to a display device, so no power sharing or balancing etc. I would have thought a MUX would work without issues, whereas a laptop without one might have issues, which is the opposite of what you are experiencing so...
I must admit not knowing much on the subject as I don't use performance laptops, just heard reviewers extoling the virtues of an included MUX.
Whether it is the cause of your problems remains to be determined though, might be a red herring, maybe the port on the laptop is lacking in some way? Is there any info you could gather from the manufacturer or their user forums, if they have them?

Which input are you using on the C1? I have the 55" myself, though it is in another room - but ISTR Vincent of HDTVTest saying something specific needed to be done with newer GPU-based machines. His channel is on YT, I'll try to take a look, but have a look yourself, maybe you'll find it faster than I.

AHA... I finally found the solution. It was a combination of things, and now I outputting 4K HDR at 120Hz! Here's how I did it: