Plasma/KDE's virtual desktops are working for me, as 3x3, 4x4 would be too small in the widget which shows in the 'taskbar', which is only 24 pixels high, here.

Took me some time and asking in their irc-channel, but actually the basic setup is super-simple, and was too 'intuitive' for an old greybeard like me :-)

You right-click on the launcher icon, or the systray and "Add or Manage Widgets", then a window appears where you can pick all sorts of widgets in a bar to the left, which then appear in a subwindow to the right. You just want the Pager, and remove any instances of that Activities Pager thing, if it is/they are already present(because you can have multiple instances in different places(leftover from earlier tries, maybe)).

What I didn't get was that you can pick that pager-widget from the subwindow, and move it anywhere you want it to in that whole taskbar-panel(outside the edit window!), by holding the mousebutton down(drag), until it is exactly where you want it, and then releasing the mouse-botton(drop).

And then "Exit Edit Mode" in the still open window, which then closes. That's all there is to it.

(Similar to how you customize the appearance of Firefox)

From then on you can configure the pager by right clicking onto it, and virtual desktops in system settings like you want them. Maybe having it appear larger with some key-combo, or whatever.

During the time I cursed it, I discovered the activity thing isn't really active anymore, they just let it there for the people who want/like it, meanwhile the real virtual desktop thing didn't get much attention, but that may change in the future?

Hopefully?

Edit: Actually the most logic sequence of things to configure would be to first go into System Settings -> Window Management -> Virtual Desktops and configure how much of them you want, and how they should be arranged.

Then activate and position the Pager like I described above, and after that how it presents them.

Nonetheless I'm thinking that could be more integrated, and the pager could be larger, when howering the mouse pointer over it.