Ok after much research and testing last night. This seems to not be theme specific, i.e. I have the same issue in Crocal.
The videos play fine as a background to a row.
But no matter what I do to the video it won’t play using the video shortcode.
This is with sound off, controls off, loop on, autoplay on.
If I turn controls on it will be fine, but obvs this doesn’t look as good.
This is only in iOS, but regardless of what browser I use. And its not low power mode.
Desktop and Android are fine.
I found this apple article, but it’s a bit above my head.
I’m sure this worked some time ago, but maybe I’m confused.