After upgrading ubuntu version from 18.04 LTS mate to 20.04 LTS mate, I came across an embarrasing issue. Workspace selector doesn't allow more than two workspaces. I can change number of rows, number of workspaces but I don't get more than two.
here's UM 20.04 on a VM, 8 workspaces, you can see them at the bottom panel.
(I clicked on Workspace Switcher>Preferences, increased #workspaces to 8)
That should be. But the box with the list of workspaces in my case doesn't appear. Weird. It worked fine in the last UM 18.04 before dist upgrading.
I reply myself. As long as I'm using Compiz, workspace selector function is a Compiz feature. Solution is in this webpage: http://ubuntuhandbook.org/index.php/2013/07/change-number-of-workspaces-ubuntu/