That seems weird, not much we can do on our side that I know of.
Best to ask the platform host on how they deal with it on their other games
could we somehow make our game cover full screen of that iframe?
If fill mode is set to Fill Window, it should be doing that already.
It sounds like you have this issue? Prevent iframe from scrolling parent container · Issue #7134 · w3c/csswg-drafts · GitHub
Our documentation pages iframe builds and don’t have the problem you are mentioning: Animation without State Graph | Learn PlayCanvas