Yes. Online sportsbooks each operate with their own rules regarding maximum bets size, but they all do have a bet and win limit. The terms and conditions at DraftKings Sportsbook, for example, state that the platform can restrict bets where the potential payout exceeds $500,000.
Other platforms, like FanDuel Sportsbook, use different maximum payouts for different sports. Bettors can find more information on betting limits and maximum payouts in the terms and conditions of an online sportsbook.