How do I prevent website from scanning during a game app?

That is how the game funds itself. Contact the game developer, as this is either a feature of the game itself, or of the game’s selected ad network(s). Or you can stop using the game.

BobHarris wrote:

It is more likely a sophisticated web popup that is pretending to scan, and in reality is just a advertisement.

There was a different game-triggered website faking a scan a week or three back.

Here’s that other recent example: trafficshield.xyz keeps popping up a web … - Apple Community

Websites cannot scan your local files. If they could, they’d not bother with the subterfuge, and just swipe everything.

It is more likely a sophisticated web popup that is pretending to scan, and in reality is just a advertisement.