You probably will meet the below error when deleting a workspace that has Dev Portal files remaining in it:
{"message":{"message":"Workspace is not empty","entities":{"files":103}}}First, please follow the below article to try to delete the target workspace by Portal CLI: Cannot delete a workspace after enabling the Developer Portal
If the Portal CLI does not look good for you, this article will guide you to delete a portal-enabled workspace via DB. Be careful when operating the database.