Which "official sources"? What am I missing here?

I ask, because when you click on Twitter's claim about "official sources", it goes to this item that claims Biden won. But it doesn't cite anything "official", just projections by the AP and NBC.

I mean, Biden's tweet's proclaiming himself President-elect have no such qualifications, such as this won claiming "voters have delivered us a clear victory". Which "official sources" are calling it for Biden and not for Trump?

Almost no state has "officially" certified their election results. So I guess it's technically true "official sources" have not confirmed Trump as the winner, but then, neither have they confirmed Biden. https://www.fastcompany.com/90575852/when-do-states-certify-their-election-results-heres-the-full-list-as-the-electoral-college-vote-approaches

But maybe when enough states have "officially" certified their results giving Biden (or Trump) 270 votes we'll have an official result.

Of course, it's not until Jan 6 that congress counts the electoral votes (cast Dec 14) that we'll have an official official result.