This is key. The text is poorly drafted on this point, but when you think about it, it's the only sensible construction. https://twitter.com/profbriankalt/status/1347024869263876098

The importance is that Trump can't just take his powers back immediately and fire all the cabinet officers who sought to sideline him.

Anyway, once Trump objects, the VP and cabinet within the four days can notify Congress that they still think Trump unfit, and that triggers a period during which the VP remains acting president while the Congress decides whether (by a 2/3 vote of both houses) ...

... to sustain the VP's and cabinet's judgment. Congress has 21 days to act.

Since Trump now has less than 14 days left in his term, Congress can just run out the clock with Pence in place until Biden is sworn in.

Ideally, Congress would sumultaneously proceed with expedited impeachment and removal proceedings that would result in an impeachment conviction that would not only totally remove Trump from office, but—this is the added value—prohibit him from ever holding federal office again.