Third party can work on solid states. Using 2020 numbers, if every Trump voter in California had voted third party, California would have still went to Biden. But there’s an alternative result that would come out. If a third party candidate gets 5% of the popular vote, they are eligible for over $120M in federal funding for the next election. Obviously he Ds and Rs spend way more than that, but a third party could make use of that money. And it only affects the next election really.
For some reason I think it means over the underwear, under the pants.