You can still use this workspace in Dispatch, but it will be unmanaged.
This means that messages from it won't appear in your inbox on the left-hand side.
💡 You can still use "unmanaged" workspaces in Dispatch
Either press ⌘1, ⌘2,... to jump between Slack workspaces.
Or press ⌘K and search for the workspace you'd like to jump to.
For Slack admins: How to Install Dispatch.
For everyone else: How to get help installing Dispatch in your Slack workspace.