Questioning suspicious numbers is appropriate and necessary, but also keep in mind that between mail-in balloting, the coronavirus, and Trump's unique style, it's not unbelievable to see a lot of ticket-splitting, or ballots that checked off Biden for president and nothing else.
For starters, mail-in ballot was a perfect weapon against Trump, even without any shenanigans. It looped in a huge number of people who wouldn't have bothered to vote otherwise, people with no strong opinion or position other than disliking Donald Trump.
The marginal effect of mail-in balloting could easily have been huge, given the coronavirus and its effect on everything else. It obliterated everything else that might have made indifferent voters think the incumbent did a decent enough job on bread-and-butter issues.
Along comes the mail-in ballot: an incredibly easy way to fill in a couple of circles to express displeasure with the guy in office during a world-shaking disaster. As easy as filling out a restaurant comment card to complain about slow table service.
Ticket splitters are also not unbelievable, although it might be hard for passionate supporters of President Trump and/or the GOP to imagine voters delivering an astounding Republican performance downballot while also ticking off Biden at the top of the ticket.
Trump can claim some amazing achievements in policy, diplomacy, and politics - we should hope other Republicans study them carefully, especially the inroads he made with so many demographics in the 2020 election. It's silly to pretend his style doesn't also alienate some people.