The only reason why I'm a gnome user, it's because of that.
And yes, I know I can just customize, but everytime I try, it just make KDE more sluggish for some reason, and doesn't really feels natural.
Not saying you're wrong, just that it's interesting how much perspectives differ on design, I suppose.
Having as much whitespace as possible and icons over text does not a modern application make.
Oh no I just checked and they also drank the kool-aid. Seems like you can turn it off at least.
But talking about real UI/UX, I do guess it's just about everything. It feels like the UI/UX was developed by programmers. It feels unpolished.
Border radius, paddings... A lot of things there being square and not round... The default icons. The context menu being to square, again. Even the default close/minimize buttons.
Like, UI wise, Finder and Nautilus is just way ahead than Dolphin for me.
Libadwaita apps also feel very consistent. I can find most of my apps with basically same consistent design on gnome.
UI wise I find gnome beautiful, their problem it's with UX and the excess of simplicity, like removing real features from Nautilus...
But at the same time I guess, KDE made the mistake of being too much complex UI wise. Even their screenshot tool it's a little insane hahahah
Maybe I just find it KDE ugly because I got super used by Gnome, macOS and Windows 10/11 UI? Likely.