You are the one claiming there was a credible threat, so it's upon you to show it.
Empirically, Facebook's denials when it suited them suggests they did not feel any such threat. The fact that they sometimes agreed is not an affirmative indication of such a threat, as they could have easily done so on the merits of the requests.
The fact that the proposed action would require Biden to collude with the GOP congress to censor speech the GOP congress supports most heavily and would never censor, combined with the knowledge of reality that such collusion would never happen, suggests that the threat could not exist even theoretically.
So, now's your chance to put forward an alternative case for there being a credible threat, rather than just an angry dude impotently swearing at social media with no actual power to repeal section 230 short of said implausible collusion. After all, Biden political appointee or not, he and I have exactly the same power to convince the GOP to censor the speech in question: None. Are my angry requests to Facebook similarly plausibly "threatening"? Obviously not.