MOV is Apple's QuickTime container, used by macOS and iOS for screen recordings and the iPhone Camera app. Structurally very similar to MP4, the two formats share most of the same internal codecs (H.264, HEVC) and can usually be losslessly remuxed between each other without re-encoding. Universal compatibility, slightly favored on Apple platforms.
How to open
QuickTime Player (macOS), every modern video player. Some older Windows software may not handle the QuickTime container, converting to MP4 fixes it without quality loss.