Turn On or Off Automatically Hide Scroll Bars in Windows 10 UWP Apps | Windows 10 Tutorials
Starting with Windows 10 17083, Microsoft has added a new setting for those who would prefer their scrollbars stay always visible in UWP (XAML) apps. Turning this setting off will result in the scroll bars in UWP (XAML) apps persisting as scrollbars in their full expanded size, even when not interacting with them.

Start won’t follow this setting yet in build 17083, but Microsoft is working on it.

Starting with Windows 10 build 17110, Start will now follow this setting.