"You have closed registrations on mastodon.social, so how will my friends get in or find me?"
Tell your friends to sign up on https://knzk.me/about then tell them: "Search for MyUsername@mastodon.social" and voilà, you have found each other.
It's very similar to how e-mail addresses work.
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko