Who is to say Trump didn’t win the popular vote?
Absentee ballots generally are not counted if the margin of difference is greater, or close to, the difference in results.
Absentee ballots, I am told usually break Republican quite heavily.
In California alone, I believe there where something like 1.2 million absentee ballots
Do the math.
All ballots cast in accord with the law are counted, at least officially. No state admits leaving valid votes uncounted. That’s why it usually takes several weeks at least to certify vote totals.
A lot of absentee/mail-in ballots fail to meet requirements, and that has lead to a lot of people jumping to wrong conclusions.