From Nitter Matrix chat:

basically, it demands that I:

1. Permanently take down nitter.net and the GitHub repository, and delete all “X Data” in both 2. Stop all use of the “Twitter” and “X” marks 3. Cease all access to X data, including copies 4. Delete all X account credentials and session tokens 5. Confirm compliance in writing within three business days

The claims asserted are breach of X’s Terms of Service, Developer Agreement and Developer Policy; the Texas Harmful Access by Computer Act; and the Lanham Act. It threatens litigation against me personally. X states it has also sent notice to GitHub and to my domain registrar.