Thanks for taking the time to post this question today.
While there isn’t a way to have an interactive scrollbar on your mockup (we don’t want to do anything that you couldn’t do on pen and paper), there is a way you can make it look like it’s scrolling.
If you duplicate your mockup a couple of times, you can show different scroll states, and then link between them to make it look like you’re scrolling.
It’s a hard concept to walk through over text, so I’ve attached a demo project file and PDF to demonstrate it. Please let me know if you have any questions.
Scrolling.bmpr (138 KB)
Scrolling.pdf (349.5 KB)