Linux desktop hasn't changed appreciably since the advent of Windows 2000, perhaps even NT4. That's 1996 or 29 years ago. XP changed the color of the start button and rounded the edges, and Windows 8 had a purple theme but it's been a remarkably consistent design. I think the only reason Microsoft has made any changes to the start bar is so that the marketing department had something visually different to show consumers, since it's such a central part of the GUI. KDE and XFCE are so similar I often forget which one to install on a new computer.

The only improvement I've seen has been for mac they have the command+space launcher which is functionally like the win+type the app you want. Graphical file browsers haven't changed since the original Mac and/or Win 3.1. Mac has never had a good tree view IMO but they do have a version of it.

The only reason UIs would change at this point is to keep UI/UX folks employed and busy, and give the marketing department something new to talk about.

Sure, why not? My desktop environment hasn't significantly changed since I first set it up in 2007. The screenshots here[1] span more than 20 years (XFCE 4.0 was released in 2003) and, aside from different user-selected theming choices, look substantially similar across that whole time.

[1] https://xfce.org/about/screenshots