3 course menu, al carte, buffet etc. what do you call these "dining format"?

In catering and the restaurant industry, these are referred to as types of "meal service."
"meal service"

In a broader cultural context, they are referred to as types of "meal structure."
"meal structure"

Speaking from a restaurant manager's point-of-view, I would use service to depict different ways of serving a meal.

For example, the traditional fine dining experience of being served one course at a time was called Russian Service, and contrasted with French Service, which involved all the dishes being served at once. Family Service is used to describe the method of serving bowls of vegetables and potatoes for the diners to serve their side orders themselves onto their plates, as opposed to Silver Service, in which the waiter will serve vegetables etc onto the diner's plate, where the meat is often already present.

So, for your examples, I would use Buffet Service, A la Carte Service, Table d'Hôte service.

I think you are making this too hard. I dine at several restaraunts that offer prix fixe or a la carte. On the menu we usually see [meal|dining] format.