This was on PC using Chrome
for me it shows this error:
Uncaught (in weight-of-a-warrior?...o_load=true&embed:1 promise) NotSupportedError: screen.orientation.lock() is not available on this device.
this sounds like a function normally used for phones and similar devices that can rotate the screen.
I was able to fix this error by accessing the game from outside a collection. If the game is accessed through a collection, there'll be a sidebar on the left with other games which seems to block the fullscreen mode for some reason. I think this is more of an issue with itch itself than the game