In Avengers: Endgame, is the snap simply dramatic, or does the wielder of the Gauntlet needs to follow this ritual to actually activate it?
It's a figurative action.
I recall Thanos saying well before he obtained the gauntlet that he just wanted to solve the problems of the universe with a snap of his fingers.
Other power-related actions didn't require a finger snap, only dramatic gestures - and even those probably aren't strictly needed.
There are multiple times throughout Infinity War that Thanos used the power of the gauntlet without snapping his fingers; sometimes he just points the respective stone at the object he's controlling and sometimes he just closes his hand. The fact that he decided to snap his fingers to use all of the stones is a formality that he imposed himself.