In a mixing bowl, combine graham cracker crumbs with melted unsalted butter until evenly coated. Press firmly into the base of a trifle dish. Chill for about 15 minutes.

Chill a mixing bowl for 5 minutes, then add heavy whipping cream and beat at high speed for 3 to 5 minutes until stiff peaks form. Set aside.

In another bowl, beat softened cream cheese until smooth, then gradually add powdered sugar, key lime juice, zest, and vanilla. Mix until creamy and well combined.

Gently fold whipped cream into the cream cheese mixture until just combined, creating a smooth and airy filling.

Layer half of the creamy key lime filling over the chilled crust, add graham cracker crumbs, then repeat with remaining filling. Finish with more crumbs and zest.

Cover with plastic wrap and chill for at least 120 minutes before serving.