Open the sample file or use your own. Start with a design that has a source artboard and an artboard to overlay it. For this design, we created an artboard with a pop-up menu in front of a rectangle that has a Background Blur applied. The background blur will soften each underlying artboard the overlay is applied to and help draw attention to the menu.
Switch to Prototype mode to wire an artboard or object to the overlay artboard. Try different Transition settings to find the animation effect you like. Use Desktop Preview to test the effect.