“Double down” comes from blackjack, where you double your bet with a confident...

https://idiominsider.com/talking-odds-at-work-the-risk-idioms-every-english-learner-gets-slightly-wrong/

“Double down” comes from blackjack, where you double your bet with a confident hand. In English, it means to commit fully, even if risk is high. Common learner slip? Saying “double up” instead—different meaning, don’t confuse the two. Keep your bets clear