There are legal avenues in many jurisdictions for slander or libel. Ultimately, though, who cares what someone posts about you and how could we expect some arbiter to decide exactly what is okay to post, especially when the concern is potential libel?
Yep, libel laws are a rule that gets enforced by the government and the platforms should be liable to follow the laws. But the post I’m responding to asserts that people should change platforms- which is not a solution that addresses the issue at hand.