I just tried this on my rig - M1 Mini, 16GB, Big Sur, everything current. New project set to 3840x1920 @ 29.97 - threw a few generators and titles in there... it's strange. The project behaves like a normal non-360 project while editing. When selecting the project file in the browser and checking the inspector, it shows the settings as above (no 360 indicated). If I then hit the 'Modify' button to change the settings, it appears to be set to 360 monoscopic (with the mono/stereo dropdown greyed out). Hitting 'Cancel' leaves the project unchanged, as expected. Exported ProRes files are square pixel and contain no 360 metadata. Maybe just a display bug?
If I set the resolution to 3840x1920 and export the video, it plays like normal in Quicktime and other players (plex, infuse etc.), however when I upload the same exported video to YouTube it treats it as a 360 video, which means there is some 360 metadata in my exported video file. Any idea how to verify the exported video is or isn't a 360 video?
I'm using Invisor to check extended metadata, and after another test this morning I'm a bit more baffled.
Took the same timeline and exported 2 files - one with the original settings and one where I hit 'OK' to the 360 assumption in Final Cut. The inspector indicates 360 next to the color space on the second instance, but not on the first.
Checking these two outputs with Invisor doesn't show any meaningful differences, but they do both show a Pixel Aspect Ratio of 1.000, and a Display Aspect Ratio of 2.000 - any other resolution, Pixel and Display aspects are both 1.000.