Plugged in an additional monitor
is it possible to have
extended screen on all workspaces
If you want to extend your workspace on both monitors - System settings > Displays, disable Mirror Display and you can have extended workspace on both monitors. You can modify it by dragging both monitors top/bottom/left/right in order to fit how you want the space to be arranged.
I think this is what you want (execute in terminal)
gsettings set org.gnome.mutter workspaces-only-on-primary false
Works same as on gnome since it's based on gnome.