In Don't Look Up (2021), Kate speaking to Dr Randall and Dr Teddy:
Kate: Oh, Randall. God. Where's Brie Evantee? Shouldn't you two be playing footsie in a restaurant that only serves cubes and foam?
What does "serves cubes and foam?" mean?
This appears to be an allusion to "nouvelle cuisine", a style of cooking that emphasises form and presentation of food over its nutritional value. Such cooking might use cubes and edible foam to create an artistic presentation of a dish.
It is obviously an exaggeration, but the suggestion that the speaker is making is that at this kind of restaurant you get a tiny (but perfect) cube of food, which is presented beautifully with some kind of edible foam. Such restaurants are thought to be exceptionally expensive, especially considering the amount you get to eat.
Taking a girlfriend to a famous and expensive restaurant is a place that rich people might go on a date. So Kate is saying that she thought that Randall was on a date with Brie at an overpriced restaurant.