Are they actually looking at the QR code (printed or on a screen) or are they actually scanning it?
I think it will take a couple of weeks for these venues, especially private establishments like restaurants, to figure out what they're suppose to do and how they will execute.
For instance, are they prepared to turn away patrons? Typically you go and sit on an open table and they bring you the menu. Now do they have someone at the door that you have to go to request a table and they will vet your pass sanitaire, either the literal pass or pseudo pass sanitaire such as US CDC cards?
QR codes are used all over the world and its a pretty simple scan and go. You just need the same software "app" on both ends to handshake. Many of the places I have been to have switched to QR codes for menus even.
Asking for ID is also pretty standard depending on the situation, this is not much different (any place with pre-paid tickets will ask for ID). I don't know why people seem to think this will somehow up-end a business. Scan and go, the app does the work. Green good, red bad. Move on to the next person.
I think it is pointless to speculate on if some restaurants want to break the law or not (I really doubt any major attractions will risk it). Will you call the place up and ask them if they are willing to break the law or just go on down the street and try place after place until you find a place that will let you in? I for one don't want to deal with such things and would be happy to follow the law as I am fully vaccinated.