But every Linux distro has its own UI, and pretty much every distro makes it easy to configure it to look how you want, with tens of thousands of themes out there developed over the past 20 years by people wanting their os to look a certain way.
The most glaring inconsistencies are going to be user-inflicted. If I spend a weekend tweaking defaults to look just right I need to be ok with possibly tweaking any new software I download to fit my theme.
But even from a non-power-user perspective, if my mom runs into problems with her computer it's much easier to walk her through a fix over the phone if she's on Windows or a Mac.
My dad, who is very tech-literate, once tried Linux and all the trouble shooting guides required him to open a command prompt (because there isn't a consistent GUI you can use to fix things across distros). He never forgave it.
You can run KDE but depending on the app and containerization you open you'll get a Qt environment, a Qt environment that doesn't respect the system theme, random GTK apps that don't follow the system theme, random GTK apps that only follow a light/dark mode toggle. The GTK apps render their own window decorations too. Sometimes the cursor will change size and theme depending on the window it's on top of.