Well, SCOTUS didn't give POTUS license to do that, but they did give license to do something awful and then have their defense team argue that the act was a part of official duties, with a chance that a judge, possibly appointed by the President, agrees.

The thing about Biden, since you brought him up, is he's unlikely to test this in any meaningful way with regards to Trump. Could he theoretically now have the USSS detail in charge of babysitting Trump indefinitely detain him, without consequence? Maybe. But he still has at least some belief in the process and won't do that.

This gives me flashbacks to lessons about von Hindenburg. An old guard who had belief in the process going by it even when dealing with someone who has obvious and sneering contempt for that process.