[Author here]
> It never really feels like it fits correctly though to call Plasma the windows-alike when talking about Linux desktops though, because the obvious alternative is Gnome.
I don't see that at all TBH.
> Initially, back in the Gnome 1/2 days Gnome was closer to Windows than KDE
I did not use GNOME 2 myself, although I played with it. I did use KDE 1 and 2 heavily. I strongly disagree with your statement.
> and in terms of /appearance/ KDE was long the more Mac-like of the two.
Not even slightly, no.
Aspects of KDE that resemble MS Windows:
* window controls at top right (not some right, some left)
* menu bars inside windows (not at the top of the screen)
* ubiquitous keyboard navigation, with shortcuts highlighted
* hierarchical filer window with tree on left, contents on right (macOS was never primarily hierarchical and never had a 2-pane view)
* main desktop focused around a taskbar
It is these days possible to customise KDE into something which is a poor, rather ugly facsimile of the Mac, but no, it is not and never was Mac-like, or Amiga or GEM-like for that matter.
In terms of the ability to have multiple panels, the use of HTML to render filer window contents, the default choice of single-click to open, it's visibly specifically Windows *98* and not 98, NT 4 or anything older. But Win98 was the current release when KDE 1.0 came out in... 1998. This is not a coincidence.
Don't be distracted by chrome. Ignore cosmetics like theme, fonts, gradients, tints. Look at the functionality.
> Gnome 3 obviously went weird, but I don't think it became more mac-like
I'd say more iOS/iPadOS like, myself.
> (except in relation to Spatial for the file explorer).
GNOME has never had a spatial UI in the way classic MacOS did. No other OS has, including Mac OS X.
> So far as Plasma goes, whether the taskbar sits at the bottom, top, left or right has been configurable for quite a while
Irrelevant: the same is true of Windows 95 from the first release.
> although the default seems to be the bottom.
Same as Win95.
> On Plasma 6 I notice that unless there's a window overlapping the taskbar it floats slightly, similar to both Mac and newer Windows.
Yes. Win11 apes MacOS, KDE apes Win11.
> The one thing that remains definitely windows-like is a start-menu type button on the taskbar, which Unity avoids
Exactly.
> (Mac, Windows, Gnome, Unity all have their own flavours of status area,
Not really, no.
GNOME is trying hard to kill it. Mac and Unity let indicators join the menu bar, but there's no separate zone.
> Gnome 3 initially tried to have the activity chooser approach
It still does.
> they re-added a start menu
No, they did not. No such thing in stock GNOME or in Ubuntu customised GNOME.
> (I still get to see this monstrosity as RHEL8 has it).
Then that is a RHEL modification and I am not sure it's a stock one. It has not been in any version of CentOS, Alma or Rocky I have tested.
Take a look at the screenshots:
https://www.theregister.com/2021/11/16/alma_and_rocky_linux_release/
https://www.theregister.com/2022/05/18/rhel_86_and_rocky_and_alma/
No "applications" menu or anything of the kind here.
> What both Gnome and Plasma have long done though is remove folders from the default desktop
They all do that now, Windows included.
> This is not really classic Mac or Windows though, as both strongly insisted on putting things on the desktop.
Not in the last decade, no.
> The major Mac-ism that always seems most distinctive to me coming from Linux and Windows familiar user is the top/global menu integration, which I don't think Gnome still has.
It does not.
> They may have experimented with it at some point
Unity does, Xfce can with addins (a bit shakily), KDE can do it but not by default.
> (both Gnome and KDE have supported some version of it, not sure if it's ever been default).
Not AFAIK, never.