Why aren't my videos saving as .MP4 files?

I recently found out you could make the iPhone save videos in .MP4 instead of .MOV, an amazing revelation! I went into my settings, into camera, into Formats, and changed my setting to "Most Compatible". As I'm writing this I went back and re-checked, "Most Compatible" was, and still is, the setting that is chosen. However, when I recorded a video and went through the obnoxious process of learning how to find and transfer the videos (the Apple article related to the subject (https://support.apple.com/en-us/HT201302) cites a Microsoft link as the answer (https://support.microsoft.com/en-us/windows/import-photos-and-videos-from-phone-to-pc-198f2301-e9a7-c734-5f39-a8946a5ebc99), which in turn cites the same Apple link as place to find the answer, causing a never-ending cycle that never supplies an answer) I noticed the video was a .MOV file, not an .MP4 file. My question is this; why didn't the video I recorded save as an .MP4, and how can I fix that issue?