LawAnon here, theory based on my experience: Biden has not denied the authenticity of the emails or the content on the laptop because it is really easy to prove emails are authentic. Pictures are more difficult but still not impossible. If he denies the authenticity and they are in fact authentic and he knew it, then his denial will be impeachment material (even if he doesn’t take the stand) in a trial. He is also not commenting on the laptop in the public realm, likely because he has been advised by a lawyer that he should invoke his right to remain silent elsewhere. All of this leads me to believe that he knows he is the target of a criminal investigation involving issues evidenced on the laptop.