Absentee vote-counting often cannot start until Election Day or immediately beforehand.

Close states (margin <5%) with Election Day counting:
Alaska
Arkansas
Georgia
Iowa
Montana
Nevada
Pennsylvania
South Carolina
Texas

http://ncsl.org/research/elections-and-campaigns/vopp-table-16-when-absentee-mail-ballot-processing-and-counting-can-begin.aspx

Vote-counting cannot start until Election Day in states totaling 335 electoral votes (538 total; 270 needed to win). http://ncsl.org/research/elections-and-campaigns/vopp-table-16-when-absentee-mail-ballot-processing-and-counting-can-begin.aspx

However, some ballot processing can happen before Election Day. Here, states that don't allow any ballot processing at all until Election Day. Only 146 electoral votes. This map includes special provisions for 2020: https://www.ncsl.org/research/elections-and-campaigns/absentee-and-mail-voting-policies-in-effect-for-the-2020-election.aspx

Here is what a hypothetical map of results could look like on Election Night, based on current polls.

Democratic likely wins - 223 EV
Too close to call - 59 EV
Count incomplete - 146 EV
Republican likely wins - 110 EV

Here it is if you want to start gaming it out yourself. via @270toWin https://www.270towin.com/maps/BloYb  #2020election

CORRECTION: Vermont is in the category of not counted yet.