Preheat oven to 375°F. Cover a rimmed baking sheet with parchment paper.
Mix broken pretzels with melted butter and 1/4 cup sugar in a bowl. Spread on prepared baking sheet.
Bake for 8-10 minutes until fragrant and lightly golden. Stir halfway through. Cool completely until crisp (about 30 minutes).
Using a stand mixer or hand mixer, whip cream cheese until light and fluffy, about 3 minutes. Add remaining 1/2 cup sugar and vanilla if using. Beat until smooth.
Drain pineapple thoroughly in a fine-mesh strainer, pressing gently with a spoon. Let drain 15 minutes minimum.
Fold drained pineapple into cream cheese mixture until well combined.
Gently fold in whipped topping in three additions until mixture is light and fluffy.
Cover and refrigerate for at least 2 hours or overnight.
Before serving, break pretzel mixture into small clusters. Fold 3/4 of pretzel mixture into the fluff, sprinkle remaining on top.