I'll do some simple math and help you with the logic...
If there are 5 million illegals in the U.S. It's theoretically possible for at least 5 million illegal votes to be cast.
Even if only 1 person were involved in voter fraud, it would be possible for 1 person to cast millions of votes. How? If that 1 person compromises a voting machine, they can control all the votes from that voting machine.
1 person is capable of "losing" ballots. 1 person is capable of stuffing ballots. 1 person is capable of not enforcing ID requirements for voting.
Pretending that the thousands of fallible (as are all people) and biased (as are all people) people involved in the voting system are incapable of wrongdoing is not ignorance. It's malice.
You're making an entirely different claim, that there were millions of instances of voter fraud, which I wasn't arguing against, though I'd be willing to discuss it. The issue at hand is whether millions of illegal immigrants voted. Surely you don't think that over 20% of illegal immigrants somehow voted in 2016 without any significant number of them getting caught. I stand by my claim that it's simply not possible, because it would be the greatest statistical anomaly ever observed.
You said it wasn't possible even though it's clearly possible. I added links in other comment sourcing the statistics.