I’m not quite understanding the question (probably due to my lack of English skills) but if you’re asking if it’s implemented in the macOS equivalent of Qt/GTK(which probably means AppKit), yes AFAIK it’s true.
That was my question. So macOS has one blessed toolkit working nicely and everything else feeling "wrong". So this has nothing at all to do with being "fragmented" but simply says "apple has one good toolkit and lots of bad ones".