If it’s 306 for Biden, it looks like any three of the five, AZ, GA, MI, PA, WI not being able to cast electoral votes brings it to House contingency vote.
If it were PA and either GA or MI that would be 36 and not enough by one electoral vote.
So it looks like any three of the five not able to cast electoral votes does not give Biden a majority.
FROM THE 12TH AMENDMENT:
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; .....
What if there is a scenario that the Supreme Court rules a slate of electors was appointed fraudulently and that such appointment was never valid. It may not be clear. Does the magic number of 270 decrease?