Applies to Biden too and all past presidents?
IMHO, they can be prosecuted for acting outside their authority granted from the Constitution, but not for doing things within their Constitutional authority.
Here's the meat and potatoes from the SCOTUS opinion:
The President enjoys no immunity for his unofficial acts, and not everything the President does is official. The President is not above the law. But Congress may not criminalize the President's conduct in carrying out the responsibilities of the Executive Branch under the Constitution. And the system of separated powers designed by the Framers has always demanded an energetic, independent Executive. The President therefore may not be prosecuted for exercising his core constitutional powers, and he is entitled, at a minimum, to a presumptive immunity from prosecution for all his official acts. That immunity applies equally to all occupants of the Oval Office, regardless of politics, policy, or party.