MajorGeeks published a quick tutorial about hiding the scroll bars in Windows 10 applications.

Disable or Enable Automatically Hide Scroll Bars in Windows 10 Apps

Windows 10 UWP apps will hide the scroll bar by default, a minor annoyance to some who prefer to have a visible, easy to click scroll bar. Here's how to get the old-style scroll bar back in your UWP or Windows Store apps, including your Start Menu.

Disable or Enable Automatically Hide Scroll Bars in Windows 10 Apps - MajorGeeks