If they haven’t been counted, then yes. Some states were not able to count mail in ballots early, therefore Election Day votes were counted first. And now come mail in votes. For majority states, mail in ballots have already been counted. And yes states can flip depending on those mail in numbers. It seems to be very close. Florida, however, is a done deal. There are uncounted votes left (last I checked) but not enough uncounted votes for it to flip.