If there are 10 people including you and the majority chooses who gets to be president and the vote ends up as 5 for Biden (including you) and 5 for Trump. Then the vote gets recast and the only thing that changes is that you decided not to vote for Biden, it would be 5/4 for Trump and the person responsible for electing Trump would be everyone who voted for him and you. If you had voted against Trump instead of abstaining, he would not have become president.
That’s a very basic concept and it’s clear that it extrapolates to the actual election.