The Blender UI elements are incredibly small by default on high resolution screens on Windows (15" UHD screen). I found the Preferences -> System -> DPI setting which can be set up to 144. This makes Blender usable, but still uncomfortable and difficult on the eyes. Is there a way to make the UI elements even larger?
Another thing that is very useful is to hold down Ctrl and the Middle Mouse Button to rescale various panels. This is the same for the 3D Viewport when zooming in or out to view a model. The Outliner Area is the only place I've found so far where this does not function yet.
By pressing the HOME key on your keyboard, you can reset the resized panels back to the original default size.