So is there a way to prevent someone from selling your stocks if the economy tanks?
You can read the prospectus that comes with each of your investments. It will describe how it is managed pretty early in the text.
Almost any low fee index fund isn’t going to be active enough to lock in losses. To my knowledge, it hasn’t happened to any of the algorithm run ones. It could happen, but it’s quite unlikely, and it would likely result in immediate legal action requiring the algorithm owner to provide some remedy to those hurt. An index should rebalance, but should never exit the market.
And while a “target retirement age” fund could technically sell early and lock in losses, that would be an actual prosecutable crime. So as long as your provider isn’t running an outright scam, with a plan to flee from the law, you’ll be fine with a target retirement fund.