Private companies can of course choose to host whatever they want. And it's certainly not possible for Github to behave unconstitutionally because Github is not

Private companies can of course choose to host whatever they want. And it's certainly not possible for Github to behave unconstitutionally because Github is not the government. But... the fact that speech was removed from a platform in obvious response to legal uncertainty created by the government, puts OFAC in serious hot water. When it comes to First Amendment issues, modern SCOTUS decisions have been extremely focused on "chilling effects". And it's near undeniable that Github's removal based on the timing was a consequence of chilling effects created by OFAC action, whether intentional or not.