If you've seen the following message, it means that your Google Workspace domain administrator has not yet enabled YouTube:
Sorry, you can't access YouTube with your Google Account. Your access has been restricted by your administrator.
How to add YouTube as a service
Only your domain administrator can enable YouTube on your domain. Let the domain administrator know that you'd like them to add YouTube as a service.
If you're the domain administrator, find out how to add services to your Google Workspace domain.