Some students asked me why his macOS app window had an extra scroll bar and how to fix it. It’s actually quite simple, and you’ll get it by the end of this tutorial.
The cause of
When you use an external keyboard or mouse, a redundant and ugly scroll bar appears on the right side of all macOS Windows, which is very impressive and causes distortion of individual Windows.
repair
Simply go to System Preferences -> General and show the scroll bar when it is set to scroll.
