Federal and state laws do protect a variety of different types of personal information in particular contexts, but there isn't really any information that is necessarily personal and protected from disclosure in all contexts.
For instance, the Health Insurance Portability and Accountability Act generally protects a person's health records from unnecessary disclosure, and the Federal Education Rights and Privacy Act generally protects a student's educational records from unneccessary disclosure.
But that doesn't mean that all of an American's health information is protected, or that all of the information that a hospital holds about an American is protected. The hospital can typically disclose the fact that it is treating a specific person, and if that person provides his health records to a government employer, that employer may be required to produce them in response to a request under the Ohio Public Records Act.
But that doesn't mean it has nothing to worry about. Like any business in the United States, it is prohibited from engaging in deceptive trade practices, so it can't make broad promises to protect users' privacy when it has no intention of honoring them. That's why it ended up paying $5 billion for privacy violations in the past and remains under court orders requiring it to better protect users' data.
Further, Facebook has users all over the world, so it is required to comply with the international privacy regulations like GDPR that can be far more stringent.