Preheat the oven to 350 degrees F (175 degrees C).

Stir flour, oats, and 3/4 cup brown sugar together in a medium bowl. Cut in butter until mixture is crumbly. Reserve 1 1/2 cups of this mixture and press remaining mixture into the bottom of a 9x13-inch pan.

Bake crust in the preheated oven for 15 minutes.

Meanwhile, beat cream cheese with sweetened condensed milk in a small bowl until light and fluffy. Stir in lemon juice and spread mixture evenly over prepared crust. Empty cranberry sauce into a small bowl and stir in cornstarch and brown sugar. Spoon over cream cheese layer. Sprinkle top with reserved crust mixture.

Bake in the preheated oven until top is golden, about 35 to 40 minutes. Let cool completely before cutting into bars. Store covered in the refrigerator.