1. "being 21" isn't a medical intervention. getting a vaccine is. I'd be equally pissed if they required me to show a statin[1] passport every time I want to buy fried chicken.
2. getting carded usually involves the server taking a quick glance at my ID. I can reasonably sure that my dining habits aren't being fed into a giant database somewhere. The same can't be said of a smartphone QR reader. If the bar was scanning my ID to check my age, I'd nope out as well.
[1] https://en.wikipedia.org/wiki/Statin