I believe the 20th is out of scope now. The 20th provides the order of succession to inaugurate a president. And it does include a backstop where congress votes for an acting president until they qualify a president or vice president.
The 25th handles the order of succession for all times during the term of the president. The current succession is Harris, Pelosi, Sen Leahy (D)
I doubt very much SCOTUS is going to go anywhere near the legislative process to elect a president - the counting of the electoral votes and stuff.
They could say that there is sufficient evidence to declare that Biden and Harris were not constitutionally certified. That puts us in very much uncharted waters. I have no idea what they would be willing to do if so.
I know this has been discussed ad infinitum but maybe there's something I'm missing above.
The fact is that once Biden was inaugurated it shut the door on just about everything other than the military.
The critical fulcrum point is whether the military acknowledges Biden is the CIC. If yes, there might be a very narrow path for Trump to fight on the grounds that Biden was not constitutionally elected. If no, then the scenarios open up a little. And I think that's why the 11.3 code of occupation is where most people are consolidating their opinion.
Most of these "I have a thought!" 1-post wonder theories are just scatterbrained. Bottom line, sit back with some popcorn and watch the show.