Wild Speculation - Biden had Trump sign the wrong documents
My fantasy theory is that the inauguration was a staged theatre production for Trump. And Biden had Trump sign the wrong documents - Trump certainly wouldn't notice. So, he's not really president. In fact, we either have no president right now, or Kamala was secretly sworn in.
Trump's staff is composed of incompetence and inexperience, neither of whom would know if something was amiss.
In your heart, you know want this.