They weren't necessarily "found." They were filled out and mailed before Election Day, and then mailed by the deadline for mail-in ballots in PA.
It took days to count them.
I have no doubt that many of them were illegal. There's no evidence to support the claim that the illegal ballots numbered in the thousands -- because the mail-in voting process makes it impossible to track them.
What happened in 2020 was that Trump was running around telling his supporters not to vote by mail. Meanwhile, Joe Biden appealed to all the losers who were perfectly content to sit at home and mail in their ballots. That's why Biden had an enormous margin in the mail-in ballots that were counted after Election Day.
They weren’t necessarily “found.”
Yes they were and Pa violated their own election laws. Their own rat SC found that to be true but the thousands of votes illegal votes were counted to hand the state to Biden.