The double click pattern to edit global regions may be new to users since it’s not commonly used in web. It may also be difficult for some users to double click.
Proposed resolution
Provide a contextual menu with “Edit Global Region” option which allows user to navigate to editing the global region.
Contextual menu can be opened by right clicking a region in layers or in preview.
Contextual menu can be opened by clicking “three dots” next to a region in layers.