What assets don’t crash with the market?

I want to leave 25% of my portfolio in assets that can be made liquid as soon as there is a market crash. So ideally if the market crashes this wouldn’t crash with it.

There are bureaucratic things that make a high yield savings account harder to do, but I could potentially do them if there’s no other options. But I’m more interested in ETFs in a portfolio. Definitely not commodities or crypto. I’ve heard of things like BOXX and about Bonds of course but the share price of bonds seems to fluctuate quite a bit and fall if the market falls in general.

So what assets are insulted from a general market crash?