If I was Biden I'd let the New York authorities handle Trump. The Cult is already brainwashed into thinking the election is stolen. In a sense, this gives Trump what he wants. He is doing this mock indignation for the sole purpose of maintaining support from his horde of nutjobs while he fights the various prosecutions he faces when he leaves office. That is his intent with this silly game he is now playing.
New York probably has plenty on Trump. Enough to at least tie him up in court until he’s about finished with a non-vegetative life. Which is probably just around the corner. Soon he’ll be drooling on himself with Rudy Mascara-colored saliva, unable to utter much more than an incoherent word or two, and prosecutions against him will be overkill.
However, I think Biden needs to set up a Commission, with the same kind of approach the Warren Commission had, to investigate and prosecute the people who have helped provide cover for Trump.
Maybe start with Lindsey Graham and work its way down from there.