a false statement purporting to be fact

So if you make up some BS and try to pedal it as fact, it is not protected speech. That doesn’t make your lies facts, nor does it make them opinions. They’re just lies.

EDIT: Before anyone tries to bring up lies being spread in other contexts, this is specifically in the context of defamation, and defamation is an established exception to what constitutes “free speech” under the First Amendment.