In the case of airports, ID was needed. For restaurants I guess I could have shown any valid QR.

Same here. Only when entering a non-EU country after flying there, they checked with a scanner. Nowhere else. Not that I do a lot of risky activities at the moment, though, so perhaps I've just gotten unlucky with the places where it should have been checked.

In Berlin this is wildly variable.

Some places have no checks at all; other places you need to show one of {show the QR code, use the Luca contact tracking site, fill out a paper form}; at least one needs the QR code and a valid ID card (not sure what, but excluding the health insurance cards despite those being photo ID).

They didn’t scan the QR codes in the places I’ve been to, they just looked at them. This isn’t the first time I’ve seen cargo-cult attitudes to how the content of mobile or tablet screens relates to security.