It is possible for a US social media company to operate in mainland China, provided it complies with local regulations, including hosting its servers in China and adhering to censorship requirements.
From experience I can tell you that also means handing over all encryption keys which is a violation of most companies compliance requirements. That means creating an entirely separate org for compliance in China with entirely different b2b and end-user contracts, terms, etc... I know of a few companies that get around this only because they are more totalitarian than China and have their own circuits bypassing the great firewall. Not naming them.