Okay? In what scenario is that an issue
Apple says "With iPhone Mirroring, users can now fully access and engage with their iPhone right from Mac while iPhone remains locked nearby." And nowhere does Apple say this feature doesn't work for games.
I'm never the kind of person who discounts a feature before I even use it. And I clearly said I haven't used it.
As another comment mentioned, it appears to use the cursor position as the pinch-gesture location.