"In Pennsylvania, more than 100,000 new voters have already cast their ballots"
That's huge because new voters aren't counted by pollsters as "likely voters". The prime criteria is often "Did you vote in the last election?" or even "Did you vote in the last 2 elections?"
So you look at the left hand column of polling information from PA:
"The federal agency estimates nearly 263,000 people residing in Pennsylvania in 2022 lived in a different state one year ago."
That being said, when I get polled, they only ask if I'm registered in my current state and if I voted in the last election, not if I voted in this state.
But this article is not about a poll. They are looking publicly available PA voting records. They look like this:
Doe, John: voted in 2024, 2020
Doe, Jane: voted in 2024
PA isn't going to cross-reference their database with other states. So there is no good way to tell if Jane Doe is a first time voter or just a recent move. Either way, she is a new voter.