You can make a workspace private from the share panel. Please follow the instructions mentioned below,
- Open the workspace you would like to change to private.
- Click on the Share button on the top toolbar
- Select Specific Users (or any other option than ‘Public’) option on the share panel
- Close the share panel
Your workspace is now private and will not be able to access publicly by anyone.
Make a Workspace Private
Find out how to share a Workspace in a public channel: How to change a Workspace to Public?