Keep seeing posts of "where are they finding these votes"/"I'm sure they'll find the votes for Biden" from some
Yes, they will- for these reasons
1) They're counting mail-in votes in GA and PA.
2) They're counting them in cities
#Election2020
Yes, they will- for these reasons
1) They're counting mail-in votes in GA and PA.
2) They're counting them in cities
#Election2020

Both of these things skew these votes to be Democratic. Not least given the President encouraged his own supporters to distrust the mail-in process. It's not surprising that in many states they've skewed to Biden.
That's why Biden has closed big, big gaps. The President's leads in PA and GA presented a false impression because they'd counted more of his votes first. That's it. It's that simple.
The counter-example is Ohio. Much excitement on election night that Biden would turn it blue. He looked way ahead. But that's because there they counted the mail-in ballots (which skewed to him) first. When the election day ballots were counted, Trump pulled ahead.
But you don't see Biden or his campaign saying "well where did those votes come from? they must be fraudulent." They weren't. All the votes howsoever they were cast were legitimate. The shifting leads just reflect in what order they're counted.