FCPX 2020 HLG timeline not editing properly after Sequoia update

There is some kind of issue here. The behavior apparently changed between 10.8.1 and 11.0 about how ProRes RAW is presented if no conversions or built-in LUTs are used. Using test material from my Sony FX6 recorded simultaneously as S-Log3/S-Gamut3.cine XAVC-I internally and as ProRes RAW on an Atomos Ninja V, if both are imported to a wide gamut library, if the RAW controls are set to S-Log3 and no LUTs or conversions are applied to either clip, the ProRes RAW clip has a much lower luma level than it did on 10.8.1.

OTOH if I put them in a Rec.2020 HLG project and apply the built-in FCP S-Log3/S-Gamut3.cine LUT to both XAVC-I and ProRes RAW clip (set in RAW controls for S-Log3), both look identical. You would normally never use unconverted S-Log3 and if the built-in LUT produces about the right result, maybe that is OK for the near term.

If using third-party LUTs which are designed for HDR or which have controls for input and output, you can set the input for Rec.709 and the output for Rec.2020 HLG. That also works, but they look a little different than the FCP internal LUTs. In this case, the third-party LUTs I used were Alister Chapman's S-Log3 LUTs.

I don't think it's limited to Sony S-Log3; I took a quick look at Panasonic V-Log an it looks similar.

This will take a lot more research to fully understand it.

I made a mistake in my last post. It appears FCP 10.8.1 behaves like 11.0, and in my tests, there is no difference between Sonoma and Sequoia in handling ProRes RAW in an HDR library and HLG project. I tested ProRes RAW from about five different cameras.

ProRes RAW is a Bayer mosaic and has no inherent color profile or gamma. It must be converted to something for viewing and other processing. FCP has an automatic "fallback" conversion if you do not pick a color space and gamma in Inspector's RAW controls (at the bottom of the video pane). Normally you would select the clip in the Event Browser, then use the RAW controls at the bottom of the Inspector's video pane to pick a color space and gamma such as S-Log3/S-Gamut3.cine.

After picking that, a "log-like" appearance will show up, but if in an HDR library, this will be a lower level if only viewed in the Inspector. If you add the clip to an HLG timeline, the log levels will be similar to viewing that in an SDR library and Rec.709 project. You can then use FCP's built-in camera LUT to convert the log exposure to the color space of the timeline. You can also use third-party LUTs, provided they are designed for HDR use or have a Rec.709 input and HLG output. Alister Chapman has some free high-quality LUTs for S-Log3 conversion, which also have exposure offsets plus Rec.709-to-HLG capability.

Do not try to manually convert from a log format. Rather, use either (1) FCP's built-in log conversion LUTs, or (2) A third-party log conversion LUT having HDR capability, or (3) Let FCP do the conversion for you by using the RAW controls and picking "standard conversion," and no LUT.

If you are grading an HDR format like HLG, that implies you have an HDR monitor. If you don't have an HDR monitor, you shouldn't be using HLG, since you cannot see it to make proper grading decisions.

Once exported, HLG is downward compatible with Rec.709, but that assumes it was graded on an HDR monitor and proper exposure and color decisions made in that environment. Grading an HDR format like HLG on an SDR monitor is like trying to grade color on a black & white monitor. New MacBook Pros with XDR screens have display presets and capability for grading HDR material.

I made a mistake in my last post. It appears FCP 10.8.1 behaves like 11.0, and in my tests, there is no difference between Sonoma and Sequoia in handling ProRes RAW in an HDR library and HLG project. I tested ProRes RAW from about five different cameras.

I can confirm that with HLG and PQ HDR projects in a wide gamut library I am not seeing any difference in behaviour in FCP11 compared to FCP 10.8 with ProRes Raw from a Nikon Z9. I always use your method 3 - no LUT, Standard Conversion so basically no user action needed for initial conversion.

What are the settings for the Project you're placing the 2020 clip into?

What LUT are you applying to it?