I cringe every time I see this come up.
Because it isn't what you actually mean, and the horrible logic of it makes it easy for the Lemmy Lefties to dunk on.
Of course a 3rd party vote isn't a vote for Trump any more than it is a vote for Kamala.
What it actually is is a discarded opportunity to vote against Trump. Which is also dispicable, but actually accurate.
Everyone knows that's what you mean by this, but the Lemmy Lefties will play dumb and latch onto that logical fallacy every time.