As monitors and display resolutions grow bigger, and people grow older and presbyopic, they are likely to increase the system text size and make screens more readable. Writing code for DPI aware programs, that look good in any display resolution is a tricky business. Microsoft isn't helping by off-loading the drawing burden on individual developers so I doubt any complex program is really DPI aware. Most apps rely on automatic scaling to look decent on high DPI situations.
Scaling the display of all the toolbars and dialogs isn't easy, and one would expect the odd glitch. But why should auto-scaling make the menu bar intermittently illegible? — I wondered in vain. Thankfully the solution is simple: use the Compatibility properties of the misbehaving program and tick "disable display scaling on high DPI settings". To access this page, right click on the xplorer² program icon on your desktop and pick the Properties command.
Now xplorer² will look nice even in large size text. You can make xplorer² fonts larger using Tools > Options menu, Window page. If you use very high screen resolutions make sure all your toolbars are switched to large icons (right click on a toolbar for its menu). This will also make the addressbar input fields taller.