Didn’t expect this thread to still be active. The issue has been fixed by Epic years ago, both in the launcher and somewhat in the engine, the trick is to disable “High DPI Awareness” in the editor settings, the binary version of the engine seems to have this off by default, and on the source build I just force that function to return false so I don’t have to bother changing it for every project.
If the “Widget Reflector” trick works for you in older engine versions great, but to me it just causes the entire interface to look blurry and it doesn’t scale every element, some still remain unscaled and looks very unnatural.