here is what i found on iphone 11 now others might vary i think but overal the bottom part where says
"Audio playback" & "Video Playback" is what you need to use. seems for audio/video you could go with H.264 which is .avi format, i think. but for most surely if you got the apple format what is it
iphone 11 specs
if that doesn't work, it might be a compiler issue, have you checked if you get any errors on export?
i remember in C2 there was this "media plugin" or "video plugin" that we used to play movies/videos inside C2 and even playback some Mp3 since C2 didn't allow .mp3 format. but in order to play those files we would've used the h.264 codec inside the plugin, which was selected from a dropdown thingie on the plugins settings. Not sure now if C3 changed to much on this aspect, probably ...
im still at "placeholder" mechanics in my game, il probably hit the same snag when i go to "audio" section.
also for me on google seems that for audio codec this comes 1st result
Edited: oh wait... this is in Construct2 area... you have to playback your audio/video files using that media plugin and select H.264 format and fil in the url for file in there, there is no default way for IOS as far as i remember in C2.