"This Week in Plasma" brings the news that...
Polishing for Plasma 6.6 (due in 10 days) continues, that the Window List widget gets sorting and section headers, System Setting loses all inapplicable hardware pages, and the window manager remembers tiling padding per screen, among many other marvelous things.
All KDE has to do, literally all they have to do, is make dedicated virtual desktops/workspaces per monitor and i'd be happy. that's it. I would daily drive Plasma if they just did that.
I suspect there's something big going on that won't make it as easy as you're thinking. I'd bet it's the same reason they haven't been able to bring one-wallpaper-per-virtual-desktop back since KDE4. They focused on Activities and worked really hard on that trying to make it a thing but it seems most people didn't really cared about it, and almost forgot about virtual workspaces in the process
KDE4, funnily enough, implemented it as "entirely separate set of widgets per virtual desktop". Which would also be nifty, but I can understand why it might be hard to do.
(The desktop wallpaper? That's a widget, of a sort. It goes in ~/.config/plasma-org.kde.appletsrc along with your panels and widgets.)
-- Frost
The only DE I know that does that, is enlightenment. I really miss that feature...
I'm currently using Niri and sure it's not a DE it does an excellent job of workspaces. each monitor has its own set of workspaces by default, no configuration needed.
I don't use Dank Material Shell or any of that but in all honesty if you wrap Niri in DMS or something like it then it actually becomes a near perfect DE. Even the Niri devs now suggest you install Niri with DMS.