There's no way to send me the project link even remotely privately. That's just the nature of the forum.
However, if you put an object/emoji in the project & set it be in the front & very large, it'll cover everything and look like a black screen. If there's a bunch of text objects, for example, most people wouldn't go to the effort of finding the right one to remove. Also, unpublish the project as soon as you copy the link.
Alternatively, include "beta" in the the project title, and don't worry about who sees it...