workspaces_only_on_primary setting is suppose to make workspaces work correctly  in a
There are older articles on the internet about enabling this option, but they won’t work with newer versions of GNOME. Prior to 3.30, I was using a very similar command which was described by Greg Cordts in his post on the subject.
After upgrading to GNOME 3.30, this way of enabling the option stopped working. After reporting this to the GNOME team as a bug, two individuals provided some very useful information,
The new way of enabling this option is,
gsettings set org.gnome.mutter workspaces-only-on-primary false
The Gnome Tweaks tool provides an option to enable this in the Workspaces tab
 Correctly means the workspace extends across all monitors and changing workspace changes to the same workspace on all monitors. I don’t know why this is not enabled by default.