To keep things simple, I have been using HDR footage from the iPhone, but it does happen with all footage from any camera.
The issue isn’t with the exported projects. It’s a display issue inside the app, where the clips appear dark in the viewer. Exported projects display correctly, even if you can barely see them on the screen to edit them.
When working with an HLG project, hovering over a clip in the browser or the timeline, it appears dark in the viewer.
When working with a PQ project, the clips appear dark in the viewer when hovering over them in the browser, but they display correctly in the viewer once added to the timeline.
The issue appeared immediately after upgrading to Sequoia and opening a project that worked perfectly in Sonoma, and they continue to work correctly on non-Sequoia machines, even if the monitor is the same as the one on the Sequoia machine. That’s what makes me think it’s an OS issue and not an FCP issue.
I’m the opposite of you. I don’t have any monitors that support Thunderbolt/USB-C, but I went to an Apple Store and tested on the demo machines hooked up to a studio monitor, and didn’t have the issue.
At home I tested on several HDR monitors ranging from a low quality gaming monitor to an Atomos Shinobi 7-Inch 4K HDMI HDR monitor, an LG C3 and a borrowed Flanders Scientific XMP310, all hooked up via HDMI. All except the gaming monitor have been calibrated and are using the calibrated profiles. Normally the Flanders is used with an UltraStudio 4K Mini, but for the sake of testing I hooked it up directly to the Mac’s HDMI.
I hope I explained this OK. It’s kind of hard to write it out to be easily understandable. When I called Apple support, they didn’t even know about HDR footage and kept calling it HGL instead of HLG, and the support rep said I was teaching them things they didn’t know about.