The counting of votes begins as soon as the polls close. It is thus possible to know the outcome from the night of voting day. However, in 2020, it took more than three days for the main American media to announce Joe Biden's victory.
It is in particular the increase in postal voting which is slowing down the counting. It takes longer because it has more steps: First, there are additional checks to make sure the voter hasn't also sought to vote in person.
Then, those responsible for counting them must open the ballots and flatten them (because they have been folded) before they can place them in a tabulator to count them.
According to the New York Times, the count should be shorter than in 2020 because fewer people will have voted by mail and because the polling stations have gained experience.
In the United States, it is the media that announce the victory of one side or the other.
