I've been travelling in Europe for almost 2 months now and I have a good laugh every time I am required to show proof of vax. It's just a piece of paper that I could have printed myself, with hand written names and dates... No watermark, stamp, website, QR code...
My friends are shocked when they see it. Not one country, coffee shop, museum, shopping mall, etc... has denied me entry.
Europeans need the QR code.
So funny!

@Toddkapper none of that is needed in Sweden, where I am now - thank God. Now Norway and Denmark have followed and are doing the same. My wife however, we kicked out of a coffee shop last week during a business meeting in Zurich because her government issued QR code didn't work. So Switzerland does use QR codes and in the bigger cities they do scan them to check. unfortunately.