The French must keep their hands on the table during meals. Not the elbow/s… the hands. It is considered inappropriate to keep your hands on your knees or under the table. Planting your elbows or leaning your whole elbow and forearm on the table are both impolite and sloppy for a French.
I understand that it’s the contrary (for the hands, I mean) in the UK… I don’t know for the other major anglophone countries… maybe you can tell us? I’d love to know!
Nobody will fine you… but it’s one of the little things you can think of… to be better considered 😉