When I see screenshots with window decorators like that I always wonder if there's someone actually using an ancient computer or if the screenshots are just really really old. I tend to guess it's the latter.
this is how it looks for me: https://imgur.com/a/OXGVCsK
There is also NsCDE: https://github.com/NsCDE/NsCDE
That's way too useful and productive.
It's not a real OS if it doesn't have ads flying out when you click controls, and constantly telling you the forecast and what Taylor Swift is up to this minute.
The screenshots are using some commercial Unix wm (mwm?) or one of the free ones that copies their look (fvwm?)
I use fvwm on one of my machines in 2023, in part because I found myself on a retro kick a few years ago, so I don't think it's that weird, though it is extremely dated.
As for the old window managers (and applications) themselves, I would imagine they are still bundled with Debian. Now that Debian allows non-open drivers in their official installation media, I'm tempted to try installing it to relive some of that X11 nostalgia. (I have fond memories of xv, xfig, and such.)