Searching the iOS App Store for “midi file player” a free app called “MIDI opener” is offered.
When that’s installed, clicking on the midi file link above offers to open it in iMovie (which can’t open it) but the MORE.. button allows you to choose to open it in the MIDI opener app, which can play it.
Works on iPhone and iPad (both are up to date).
I think once you’ve opened it once in MIDI Opener, that’s what is offered the next time you click on a midi file. I guess it would work from email too.