HDR auto-switching issues in Windows 10

I am posting this for anyone having an ongoing battle with HDR content playback. When I first got my HDR Monitor, all worked perfectly. I define “perfect” as:

1. Being able to leave Windows Display setting for HDR to off.
2. Being able to then open an HDR video file with the MPC-64 player and get HDR playback automatically, either windowed or Full Screen (my choice of setting).
3. When I close MPC, I expect my desktop to default back to SDR.

At some point one of the recent updates broke this. HDR content files were now being converted to SDR by MPC Video Renderer, and my monitor was staying in SDR now even though nothing had changed. I tried fiddling with settings, reinstalling drivers for hours before I finally got it to work again by rolling back to version 1780-Mega. Good thing I save these old install files locally

For reference my PC for the above problem consisted of Windows 10 on a Ryzen 5700G processor with Ryzen VEGA era integrated graphics and 32gb Ram. The monitor is an 77" OLED Samsung TV.
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Inspired by all of this, I decided to tackle another machine that to date had the same problem, and wouldn’t pass though HDR even when the Windows Display toggle was “ON”.

After a lot of trial and error, I finally got it to work with the most recent 8565-MEGA verson. It took manually turning the Windows Display setting to ON while HDR content playback was attempted. One such try “woke up” the MPC Video Renderer. It worked, and continued work most of the time with HDR auto switching even after I turned the Windows Display HDR toggle off.

This system consisted of Windows 10 on a Ryzen 5900x, Nvidia 1060 graphics 6gb card, 64gb memory, and a 55" OLED Samsung TV.

The MPC Video Renderer settings that finally got things rolling were: (you open these by MPC Play menu –> Filters –> MPC Video Renderer)

Leave HDR pass through to Windows checked (on)
Un-check the convert to SDR option (off)
Windows HDR Pull down menu in the app: set to “allow On/off”

This is not 100% full proof. Occasionally it will “fail” and while your monitor switches to HDR the file content doesn’t output HDR correctly, resulting in faded washed-out images. Restarting another file usually wakes it back up again.

If anyone else has further insight on all this please share. I am almost afraid to allow any more updates for fear if borking my system again until I understand the problem’s real cause...

As you already found, there is option in MPC Video Renderer to allow it to turn on windows HDR.
Do not uncheck Convert to SDR. That is only relevant when passthrough is not possible, in which case you WANT to convert, or else you get wrong colors.

If switching to HDR doesn't always work smoothly, it may be due to graphics driver issues.