"what does one do when presented with QR code taped to a table? I have not the slightest idea. Anyone else have advice on this?"
OK, here's what you do. Open the camera on your phone like you were going to take a picture. Hold the camera over the QR code and center in the yellow brackets. A small name will pop up at the bottom and you touch that and poof a menu (or whatever) opens.
I suggest you practice with this at home. On the localTV news I watch they often have show QR codes with links to further information. Also on Good Morning America in the Deals and Steals section they will pop up a QR code on the screen. You can also see them in the grocery store, etc. Here's one to practice on from the local TV station. Even though the sign is set at an angle my phone would still read it.
https://www.kxly.com/want-a-yard-sign/
You do not need a special app to read these. (Editing to add this is on my iPhone. Balso has posted below that you may need an app if you have an Android phone so go with their advice if that’s the case. )
My experience in Bordeaux last Fall was that they did NOT have a paper menu available. Of course I could have gotten up and gone somewhere else but I was hungry, had a wonderful table outside in the shade facing the Cathedral and wanted to enjoy the ambiance!