This video explains how markups are created and managed within a workspace.
When you create a markup, it only exists within that workspace. If you want to share a Markup across workspaces, then you will need to publish it to Content.
Open the Scene Manager and open the three-dot menu for the markup, or selection of markups, you would like to publish.
Select "Publish", where a modal with the project's Content folders will appear.
Select the Content folder you would like to publish the markup(s) to and click "Publish".
Once published, the markup will have the permissions for the parent folder, which you can see in more detail by clicking the "Access" section in the markup's details.