The reality is that he's not. Not yet, since the Electors haven't gone to the Electoral College and still won't for a long time. In between now and then there will be court challenges.
Will those challenges change the ultimate outcome? Almost certainly not. But it's still a fact that Biden is not the President-Elect.
Should Twitter fact check people calling him the President-Elect? IMO, probably but only to look unbiased. Will they? No, because they don't care about looking biased despite 70M+ Americans siding with Trump.
It's not "biased" and never has been to project a winner based on statistical data. But if we're sticking to a statistical conclusion, how do you think Biden should be described at this point?
There is essentially no basis in history or law to believe that Biden will not take office, unless he dies before inauguration. There are no credible legal theories by which he will not be elected.
What should "people" do? The loss of faith is driven by four years of the President lying day in, day out. There have been plenty of voices throughout speaking up for truth and institutional respect, but they're baselessly attacked at the highest levels.
Will those challenges change the ultimate outcome? Almost certainly not. But it's still a fact that Biden is not the President-Elect.
Should Twitter fact check people calling him the President-Elect? IMO, probably but only to look unbiased. Will they? No, because they don't care about looking biased despite 70M+ Americans siding with Trump.