We’ve noticed that the full screen option disappears when the user agent is iphone or ipad. (It’s reproducible by opening Chrome under Linux, opening dev tools, enabling the device module, selecting any ipad or iphone and reloading the page). We’re wanting to confim this is deliberate and query what the issue is.
It is intentionally disabled on ios devices because iPhone did not support the browser fullscreen API until recently.
It is also disabled because the way iOS handles full screen mode is not very good and does not play well with navigating around a document (for example, if you move your finger in a certain way, it exits full screen mode).