Followed the instructions here:
Deleting a Workspace
But the workspaces stubbornly remain in the left nav. Despite having no issues, workflows or other resources linked to the workspaces.
The following developer tools screenshot, is from the point I clicked on the “I understand, delete this workspace” in the “Edit Workspace” display.
There’s a very brief message popup - perhaps “Unable to delete workspace” - hard to tell because within a second the workspace is refreshed.