Vote for the candidate that can win and is the least objectionable.
If you can't bring yourself to do that, at least vote third party so there's some indication that your vote is up for grabs.
If you can't even bring yourself to do that, at least go to the polls and cast a blank ballot, or only vote for down ticket races for your local elections. This matters a lot more than president at the end of the day.
But if you just don't vote at all, then you're not even part of the calculus for those newer, different candidates who might point us in a better direction. They won't know you exist as a political entity, and they won't know they can court your vote.