The relevant section from the Constitution:
The person having the greatest number of votes for President, shall be the President, if such number be a majority of the whole number of Electors appointed
The key word there is “appointed”.
That means the number of electors selected by the individual states and sent to Washington DC to vote.
If a state failed to appoint its electors in time (safe harbor date this year is Dec 8) then Congress could choose to accept those electors who were appointed, and a majority of THEM would all that would be required to elect the President.
So say Trump wins North Carolina and gets to 232 (Biden having 306).
All Biden would need to win is 233.
He would still have that if Arizona, Georgia, Pennsylvania, Michigan and Wisconsin…the key states under dispute…all failed to appoint electors.
Not that this would ever happen…but if it did, Biden still wins.
This is why there have been calls from key Trump supporters to have the states who have GOP legislatures, like Pennsylvania, to select a Trump-favoring slate of electors and send them to Washington. As opposed to simply make states miss their election certifications and send no one there.
Just a bit of political trivia there.