The most obvious and trivial answer is that countries implementing mask mandates have seen COVID become endemic. That masks provide 'some' impact is obvious. That said impact is negligible is also obvious. We are still waiting, years and years latter, for that curve to finally be flattened.
So no data, cool. I will no longer believe Johns Hopkins and will instead defer to you for medical advice because obviously you’ve made a seriously compelling argument.
Curve flattening was about trying not to overwhelm the hospitals.
You're making a basic logic error that I've seen so many times from your camp: "if it doesn't work 100% it doesn't work at all". Why do you think this is a logical requirement?