why can't - or how can - i download an .mp3 or video file on an iphone and play it back?

Oh, no this has nothing to do with anything like that. It's just the (what should be) simple act of downloading an mp3. ANY mp3. or a video - ANY video. Where does it "land" and then, how do i "find" it .. and then, how do i PLAY/VIEW it? In this case, it's a video that I made from a zoom call and sent to myself as an email attachment - so that i could simply (i thought) review it on my Iphone when i downloaded it from the email attachment. In other cases it might be a download from a "wetransfer" FTP Other times it might be an mp3 or a video someone has made and emailed to me to just, download and look at. These aren't 'commercial products' - they're just files from one location to another.

I mean..what? Does it have to be created in an "apple branded product" for me to be "allowed" to see or hear it on an Iphone LOL