You do not need to read the entirety of today's 119-page opinion in Trump v. US. All you need to read is this paragraph from Justice Sotomayor in dissent:
I think one point the people who are urging Biden to use this power forget is that this same Supreme Court is the one that gets to decide which acts are official or not
Page 2... immunity..."do not extend to conduct where his authority is shared with congress"
Seems like a whole can of worms and keeps the door open to go after Biden on immigration grounds