My understanding is that if these companies wish to use Section 230 to keep themselves from being held liable for what their users post. By censoring users' posts that don't violate the law they are acting as a publisher and not a platform, ergo eliminating Section 230 protections.
To my understanding, Trump didn't authorize the publishing of his tax info, so surely that would count as "hacked" or "illegally obtained", right? From what I've read about Hunter Biden's laptop, the information was legally obtained because he left the computer at the repair shop long enough that it legally became the property of the shop owner. I could be wrong (and if I am, please let me know) but that, to me, seems like clear bias on the part of Twitter and Facebook.
If they had treated both articles in the same manner I would likely agree with you about a lack of bias, but it seems to me that this was done to prevent damage being done to one campaign.