Hi Squarespace, if you have any definition of this problem, please let us know. Maybe we can help with creating the solution.
iPhone X (Google Pixel 4 may be a problem too, needs confirmation) All other phones work
Background video hosted at Vimeo
Background video does not auto play, only fallback image loads
Low power mode off, phones fully charged
No console errors detected
Vimeo adaptive bitrates working on other devices
The endpoints confirmed to work as expected
iPad Pro, iPad, Chrome Mac, Chrome PC, Edge, Safari
Chrome dev simulator of Google and Apple mobile devices.
Safari dev simulator of Apple devices.