Not financial advice.

The most straightforward thing to do that would have saved you in 2008, 2000 (and even 1929 to some extent), is to limit debt exposure and have enough cash sitting around so you don't have to sell your positions.

People who held (and invested more during the low points) did just fine. The people who got hurt the most were in a position where they had to sell (their 401k, their house etc) for a loss.

When a crash happens, it's a buyers market. In some ways it's a transfer of wealth to the top.

The problem is, timing the crash is impossible. Inflation chews into your cash portfolio, that could've been used to grow wealth.

Edit

There are of course more complex financial instruments. And they're interesting, but essentially amount to gambling. Holding short positions on sectors/companies is a zero sum game. As a retailer, you're betting against firms that have a lot of money and insider knowledge. Even if the thesis is correct, it has to be correct at the right moment.