Adding Workspaces after HDMI connected

Once I connect a an ext-monitor through the HDMI port to play videos in VLC, I can’t add any more workspaces. I have to first add workspaces with apps in those workspaces as ‘place holders’ in the event I want to use those workspaces and ‘then’ connect the HDMI port and play / stream videos, which becomes the last workspace. So once the HDMI port is connected, no additional workspaces can be added. I would like to add workspaces regardless of when the HDMI port is activated