Biden's biggest failure was choosing appeasement, also known as accessory after the fact in legal parlance, over justice. Of course, unfettered justice would have decimated both parties, and most of the judiciary. But bipartisanshit man has learned nothing from his decades of bipartisanshit.
The US developed this weird system whereby the Justice Department is part of the rxecutive branch, yet is somehow supposed to be independent. Biden either needed to not pick Garland, or quietly get him to quit. Pre-Trump, the idea of ordering investigations directly was supposedly beyond the pale.
... or Biden did intervene, but it was to prevent true justice from striking down "both sides" for their litany of crimes. This one's at least likely, I'm sure.
That's exactly what he did: he chose Merrick Garbage precisely for that purpose, and let Merrick Garbage betray the country from day one without even pretending that he valued justice.
He didn't have to actually order any particular investigation, all he had to do was choose a competent prosecutor and order him/her to DO YOUR JOB WITHOUT ANY PRETENSE AT FEAR OR FAVOR.