Bitcoin's correlation to the S&P 500 was just 0.01 from 2017 to 2019, which suggests equity and crypto prices were moving independently. That changed in 2020 - 2021, as the correlation jumped to 0.36, indicating the asset classes were moving closer together.
What's the implication? It means the Bitcoin and the broader crypto world aren't likely to offer protection against downturns in equities.