Final Cut Pro 10.8.1 - problem with HDR videos since upgrading to MacOS Sequoia

@IAmSkippermark: I can now see the problem. I connected my M1 Max MacBook Pro to my HDR/HLG/Dolby-capable LG C8 TV, and it behaves as you described. Quicktime playback shows as HDR, but within the FCP viewer (if connected to the TV), it does not. That is using Sequoia 15.1 and FCP 10.8.1 or FCP 11.0. Unfortunately, I don't have any machines still running Sonoma to test.

MacOS Settings>Display shows "LG.TV" as the color profile, and the HDR option is enabled in the UI.

If I disconnect the HDMI cable from the TV, the FCP viewer displays HDR. That is using an iPhone Rec.2020 HLG Dolby Vision clip in a Wide Gamut library and a Rec.2020 HLG project, with auto color conform on. I tried all combinations of color conform in FCP settings and the Inspector and none of those worked.

So when the MacBook Pro detects the TV is connected via HDMI, it handshakes and this somehow restricts the FCP viewer from displaying HDR in the MacBook Pro XDR screen or the HDMI-connected TV. But it does not affect Quicktime Player display of HDR/HLG content on either MacBook display or the HDMI-connected TV. This implies it is not an HDMI cable issue (although I'm using 8k-rated HDMI cables).

My TV by itself can clearly decode and show HDR HLG content if my TV streams it via ethernet using the WebOS Youtube app from a Youtube HDR channel.

This is a complex issue because several things are happening "under the covers." The playback app (Quicktime or FCP) reads the NCLC tags (aka code points) in the file metadata, the app decides how to handle that, then MacOS ColorSync does a match based on the display device color profile.

Simultaneously there is MacOS EDR (Extended Dynamic Range) technology which modifies the video output IF the internal or external monitor is an Apple device capable of HDR. The purpose of EDR is (1) To squeeze out the best image on an Apple display and (2) To differentially control luminance of the viewer window vs the UI elements. This avoids excessively bright UI elements during HDR playback. There are some WWDC talks on this.

I will have to do further testing and possibly run FCP under XCode to see what is happening. This could take several days.

Yes, here you go! The LG TV is the output from the Macbook Pro via HDMI.

This first show shows the TV is getting HDR from the laptop (Upper right says HDR)....

The second shot shows the output from FCP...very dark and dull. The actual laptop screen is HDR.

Media specs from FCPX...I don't have those other options you mentioned. The point is this all worked great with these clips until I upgraded to Sequoia. These are HLG shots from a SONY A7III.

Can you give the specs of the media and the project properties you used?

could you post screenshots that post the project properties, the clip into, and what you see in the FCP viewer and in the QuickTime Player.

What happens if you change your project settings to Wide Gamut HDR Rec2020 PQ? Rather than change the existing project, you can do this by Duplicating Project As....