As a recent toe-dipper into linux (now running Arch on a powerful minipc and KDE plasma) I'm shocked at how little progress has been made on the native UI side.
Windows' Metro/Modern UI was pretty good from different perspectives, but didn't have enough effort put into it to make it a universal thing fit for multiple purposes (half of the Windows settings was still in Control Panel for quite some time), wasn't familiar for users (so they hated it) and wasn't familiar for developers (so they created hideous apps).
In the opposing Linux camp, GNOME made Gtk 4 with Libadwaita UI library with "everything is a phone app" mindset that not every app can adopt. For example, there's no application menu (a line with File, View, Edit, etc.) component shipped by default, you should make it yourself or get it somewhere. So now GIMP is developed using Gtk 3 (not modern 4) because it has all the components GIMP needs. Trying to get GNOME developers to implement some stuff outside of their vision is a futile effort.