Heat the oven to 325°F and line an 8-inch square pan with parchment paper. Stir the almond flour, coconut, powdered allulose, salt, and melted butter together.
Press the crust mixture firmly into the pan and bake for 9 minutes. Let it cool while you make the filling.
Beat the cream cheese and powdered allulose until completely smooth. Mix in the eggs one at a time, then blend in the sour cream, key lime juice, zest, and vanilla.
Pour the filling over the crust and bake for 34 to 38 minutes, until the outside is set and the center has a slight jiggle.
Cool the cheesecake completely, then refrigerate for at least 4 hours.
Mix the shredded coconut, sliced almonds, allulose, and melted butter for the crunch. Spread on a baking sheet and bake at 325°F for 6 to 8 minutes, stirring once, until lightly toasted.
Cool the coconut crunch completely, then scatter it over the chilled cheesecake and press it on gently.
Cut into bars and serve cold with extra key lime zest if desired.