[Svartalfiar]

Three of the four can be magnanimous, and avoid some Democrat rioting, by allocating the EVs 50-50. If only one of the bigger 3 (PA, MI, GA) deny their EVs to Biden, by not certifying, or by giving the set to Trump, then Biden fails to get to 270 by Monday, and the 12th Amendment kicks in for the second time ever (1824, John Quincy Adams).
If MI, GA, and WI all go 50-50, and PA goes to Trump, that gives a 265-273 Trump win. If PA simply fails to certify, that gives Biden a 265-253 win.

If GA or MI is the flip and the other three go 50-50, Trump wins 271-267.

If WI is the solo flip, then Biden barely gets the win right at 270-268. There is no math with these four that sends it to the House, unless one of the States goes 11-5 or something like that to cause a tie. If all four just fail to certify, Biden wins 244-232. Trump has to gain votes from this, and he has to fully flip at least three of these States.

[Reily]

“..... If PA simply fails to certify, that gives Biden a 265-253 win. ..”

No Biden would have failed to reach 270. It would go to the House, a potential Trump win.