When you create a Link from one scrolling Artboard to another, the scrolling Artboard’s position will normally return to the top (the start position) when you play the prototype and click on that Link. This is fine some cases (such as switching between tabs in a mobile app) but not others (like when you want to display a modal or overlay, in place, on top of the scrolling content).
To make sure a scrolling Artboard stays in position when you click on a prototype Link, select the Link you’re working with and enable the Maintain scroll position after click option in the Inspector.
With this option enabled, when you play your prototype, scrolling content will stay in the same position as you click on links and transition between Artboards. This allows you to create overlay-style effects that feel more realistic and don’t interrupt your prototype’s flow.