I believe the solution for developers is to just use a banner. Not elegant, but should work in most cases. So the "side buttons" are over the banner and then the game area begins.
A sort of solution on desktop is to just tell your browser to display that area different.
This should work as a user css style.
@-moz-document regexp("^https://[^/]+\\.itch\\.io/.*") {
.user_tools {
position: static;
}
}
What also should work, is zooming in, till the button area gets flattend on top. The Itch css is adaptive to screen width. But that does not work on some games, as they need default or even lower zoom.