In November 2023, the publisher of smash-hit videogame Genshin Impact obtained a DMCA subpoena hoping to identify who was behind the leak of unreleased artwork on Elon Musk's X platform. X Corp. challenged the subpoena, citing the user's anonymous speech rights under the First Amendment. In an order published this week, a district court judge denied X Corps' motion to quash, in theory exposing the alleged leaker's identity to Cognosphere.
Accordingly, an author’s decision to remain anonymous, like other decisions concerning omissions or additions to the content of a publication, is an aspect of the freedom of speech protected by the First Amendment.
US Supreme Court, McIntyre v. Ohio Elections Commission (1995)
A quick skim says anonymity is protected under it, with exceptions. Mostly for criminal acts. Particularly here, if the leaked artwork falls under "intellectual property" then the exception applies and anonymity isn't protected.