“he would have undo what Biden did on his own.”
Wrong.
Quo Warranto (look it up)
https://code.dccouncil.us/dc/council/code/titles/16/chapters/35/
I would have to do more research to figure out if quo warranto really would overturn everything a president did, but I did find out that the Supreme Court ruled that it didn’t apply to presidential electors in State ex rel. Barker v. Bowen, 8 S.C. 382 (1876), when Tilden electors tried to get the court to throw out Hayes electors. It’s unlikely that a DC court would over turn that, especially since the city went 92% for Biden.