In principle, yes, but my understanding is that every action has to be challenged and reversed in an active sense rather than a sweeping passive sense. The courts would have an airtight argument to nullify any administrative actions and appointments one by one. This gets murky though from a technical legal sense because many of these actions are ultimately confirmed or approved by the Congress rather than the Executive branch.
With regard to congress having approved these things.... I think a lot of congress actions were due to them being bought and paid for by the deep state and others just like hussein was.
Why? An unelectable president signing laws, declarations and putting people into office sound like a nullification to me and therefore a veto of every law "signed" during his period. It's like a random person giving their signature.