There are so many volatility indices around. You might want to be specific on which kind of crypto volatility index you really need. When you check out chatting tools like tradingview, you will be met with so many of them. Maybe you can start from there.

Isn't that called CVI it is similar to VIX or a volatility index?

If you are looking for this I think better check the tradingview you can find them when you search symbols like sample Bitcoin go to the indices tab and you should be able to see historical volatility or volatility index but not all coins/tokens have this in tradingview you might need to use a 3rd party like this one below

- https://youtu.be/SXi7fDvYM9Y?si=Zmecdd__k-WjFruz