In a medium bowl, mix graham cracker crumbs with melted unsalted butter until fully coated. Reserve ½ cup for layering, then press remaining mixture into the bottom of the trifle dish.

Chill a mixing bowl and beaters in the freezer for 10 minutes. Pour in heavy whipping cream and whip until stiff peaks form (3-5 minutes). Set aside.

In a separate bowl, beat softened cream cheese until smooth. Gradually add powdered sugar, key lime juice, lime zest, and vanilla extract. Mix until creamy.

Gently fold the whipped cream into the cream cheese mixture until fully combined and smooth.

Layer half of the lime filling over the crust, sprinkle reserved graham cracker crumbs over it, then add remaining lime filling on top.

Top with remaining graham cracker crumbs and optionally sprinkle more lime zest. Cover and refrigerate for at least 2 hours.