In Green Book (2018), Oleg takes vodka from the bartender and cheers to Tony and George:
Tony: Danke schön.
Why did he say "No" in this scene?
Oleg was seeking support from Tony to what he said earlier.
Tony was wondering why someone like Dr. Shirley had to put up with all misbehaving people throughout his tour. Oleg was explaining the reason behind that and said:
Because genius is not enough. It takes courage to change people's heart.......No ?
The waiter just happened to come with the drinks in between their conversation. They took their drinks and Oleg completed what he had to say. That "No" has nothing to do with the drinks.