FFmpeg is way cooler than it sounds.
Videos shown in Google Photos typically have Loop video automatically enabled; however, if your videos are not looping, you must manually enable it. Find your video in Google Photos. Tap the Menu (⋮) ...
MOV is not one file format but rather a format envelope that can be made up of any of dozens of codecs, resolutions, and frame rates from basic DV through H.264, HEVC to ProRes, and other pro formats.