When you share a video that includes Dolby Vision HDR media recorded with an iPhone 12 from Final Cut Pro to Apple devices, it might appear to have a colour shift when viewed in QuickTime Player. This can happen if your media has extreme contrast between scenes.
To improve the look of your project when viewed in QuickTime Player — for a quality control review of a project for example — export the media as a Master File, then choose an HLG colour space when setting share options.