He didn't win 80% of the vote in PA. He won 80% of the vote in one democratic county in PA.
You must be new to following geopolitics on this local a level in the US, but because Trump's nonsense has him stumbling into the area and you crawl around smelling his farts, here you are. Since you are new, allow me to fill you in. Every American has seen these splits before. It happens every fucking election.
The western part of PA, like most post-industrial parts of the NE and midatlantic, is in a near terminal decline, and is some of the staunchest trump support I've ever seen. Some of these counties went for trump at 75% plus, some at more than 80%. When the in-person vote was immediately counted, without the mail-in vote, the margins in some of these counties were 90% Did you bat an eye at that? Was it evidence of fraud?
The only difference here was a question of narrative. There ought not be a narrative structure to counting, but because different votes were counted at different times, there was here. Otherwise this election would have never been seen as particularly close. Several states would have been called much earlier, and Biden would have probably locked up the call that night.
In PA the number of mail in votes was staggeringly democratic. More than three times as many democratic mail in ballots were requested, and a higher percentage were returned by democrats. No one really liked Biden, but a supermajority of people in most large cities in the Northeast fucking HATES trump. Add that into your model of all human behavior.