From O'Connor's opinion:
... “Regulations on self-built arms are not longstanding.In fact, there were no restrictions on the manufacture of arms for personal use in America during the seventeenth, eighteenth, or nineteenth centuries.” Thus, the Court cannot conclude that the Final Rule’s imposition of ambiguous and far-reaching regulations, which would restrict access to component parts thereby inhibiting home gunsmithing, comports with the SecondAmendment.
Which takes out one of Biden's 'rules' to make it harder for citizens to do things officially disapproved of, like making your own firearm.