Cryptocurrency and Bitcoin has bloomed since 2009, and still going upward.
Some commercial banks, including some investment banks, introduce their own cryptocurrencies for the purposes of settlements and transactions with certain financial institutions and corporations. At the moment, central banking is not interested in cryptocurrencies, but this may change in the future.
And it will definitely do.
Will just leave those banks to used blockchain technology, I think that's already a win-win for us. If they decided to developed their own crypto, aka CBDC, then that will be find. There will be no effect on bitcoin or any major crypto to begin with. It has it's own advantages and disadvantages that we average joe can benefit so why not? But if you are talking about banks investing on bitcoin? could be, they are in the business of making money to begin with. So it they saw opportunity on bitcoin, I'm sure they are going to grab it.