Thanks for flagging this, I pushed an update just a bit ago with this change. There is now a Control tab with the Sound, Full Screen and Force Update functions.
Tested in Chrome, Edge, and Firefox, but not sure how it works on Safari yet.
Was able to have a friend test the game on their iphone and made some changes, looks like the only option for them is click the Share -> Add to home screen then it plays full screen from there.
