Trump wasn't winning on election day, that's not how elections work. You win when all the votes are counted, if you loose then you were never winning at any time, it's not a fucking football game where the score changes then you have a winner.

He was only leading in the count on election day because of how skewed the different forms of voting were depending on your political affiliation. he literally told his voters not to vote by mail or early when the other side was doing everything they could to get people to vote early. Which was a really dumb thing to do during a pandemic with the gop having an older demographic, but that's another topic.

Since election day votes are counted as the day goes on when you put your ballot in the scanner, mail ballots are not counted usually until election day is done for good reason, they don't want people voting twice. So they are held to cross reference to election day voters to make sure someone didn't try to vote twice. That's the only reason trump was leading on election day, his voters voted day of, bidens voted early. So trumps votes were disproportionately high in the initial count. If mail ballots were counted first Biden would have been in the lead the whole time.