My controversial take:
Linux desktops peaked with KDE 3.5.x. (Gnome is a ghastly abomination and KDE's been going downhill ever since.)
macOS desktops peaked with Snow Leopard (10.6). Everything since then has gone downhill in UX. (Honourable exception: filesystems and backup support. But those are below the desktop level ...)
Windows never had a peak to fall off and has been subterranean for decades. Put it out of its misery and start over from IBM's mid-80s CUI spec.
Desktop computer usability has been going backwards for 20 years.
@cstross The idea that the future of Computer UI are touchscreens is an abomination I don't think I can accept.
@falken @foxxtrot @cstross Almost 30 years ago I saw Independence Day with a friend who's now prominent in game design. When Will Smith and Jeff goldblum were trying to detach from the docking port, one of the invaders in a control booth notices and operates his interface to investigate. Friend whispers in my ear, "oh no! the aliens have touchscreen technology! How can we ever defeat them??"