I took a whole bunch of videos with iPhone 12 (MGJ83ZD/A). I was able to play the videos on the iPhone, but when I tried watching the videos via Photos on my MacBook Pro (Retina, 15-inch, Late 2013), they will not play and there is a triangle with an exclamation point that says, "Unsupported Video Format - The full-resolution video is unsupported".
What is happening here?
MacBook Pro
See: Using HEIF or HEVC media on Apple devices - Apple Support
Your MacBook Pro would need to run macOS 10.13 High Sierra, at least to be able to play videos in the HVC format. If your Mac is already running macOS 1013 or a more recent system version, the High Efficiency format should be no problem, unless you have been using a very high sample rate for the videos.
What version of MacOS do you have. My guess is your mac does not support the HEVC format, or HDR video your iphone 12 is creating. It may also not support 4K video
Try changing you camera setting to shoot in "most compatible" format, and turn off HDR. If necessary also try 1080p rather than 4k.
videos won't play
