Comment by antiframe

Yes, those are all different versions of the underlying widget frameworks. I don't understand your point. My current GUI is KDE Plasma 6.6. The only libraries I have installed are Qt 6 (which I am not sure why you didn't list). I have no need for version 5 or 4, or any other. The GUI is consistent.

When I last used Windows, on a fresh install, I saw a mixture of different frameworks used for core OS components from the same vendor.

When I last used OS X, it was pretty consistent but I hear complaints from friends that its no longer the case.