If you click a link to view someone's Scratch project and receive an error message (like "Oops! The Server is Scratch'ing its head"), the project is likely not shared.
Before a project is shared, the only person who can see it is the project creator. Once they have shared the project, the project link should work for everyone, even people who are not logged into Scratch.
If the project creator is having trouble sharing their project, they might need to confirm their email address. They can check if their email is confirmed and request to resend the confirmation email in their account settings.