Single-check chess is a variant where the first person to give check wins. There is a website that claims it has been solved, with white winning in four moves; however, I cannot find the moves anywhere.
If you trust Stockfish's evaluation on lichess.org, using the "three check" variant where both sides already have two checks, White wins in 5 moves with 1. e4, 1. e3, 1. Nc3, or 1. Na3, and loses otherwise.