election results
binomial probability equation = (n!/(k!(n-k)!))(t^k) ((1-t)^(n-k))

Trump

Biden

rejected

n   mail in ballots (half of total)

k   actual rejected plus twice (1.) difference in vote

t   % expected rejection rate with inexperienced voters

NA

NA

The smallest number is the below table is 16. That is 1 in 10^16. 1 in 10,000,000,000,000,000 that it was a free and fair election. This is using the absolutely lowest, most conservative rejection rate of 3%. It should have been closer to 30%.
1 in 10^n probability that Biden actually won
percentGeorgiaArizonaWisconsinAll 3
3.0826016448916
4.0157121274143022326
5.0240703960417038707
6.0330477579779457072
7.042490118681205576896
8.052308166711680297869
9.0624442188621943119793
10.0728612744627413142533
11.0835323330433166165999
12.0944383942539170190123
13.01055674578245401214856
14.01169095235651839240163
15.01284565913358472266017
16.01402056610065287292397
17.01521537324972277319290
18.01642968057379435346685
19.01766358806586755374576
20.01891709572494235402957
21.0201901103544101872431827
22.0214829111525109663461186
23.0227957119664117608491036
24.0241287127962125705521379
25.0254822136418133955552222
26.0268565145032142359583568
27.0282520153806150917615425
28.0296690162741159630647801
29.0311081171837168501680704
30.0325696181099177531714145

(1.) Since Biden got 75% of the mail in vote, the 25% for Trump cancels out 25% for Biden leaving 50%, thus double the difference in vote to cancel that many votes.
Java and C++ versions available here:   binomial.zip or to see calculations in javascript.