Cryptocurrencies are not threats to traditional banks. Many countries banned bitcoin and all other cryptocurrencies in the past but after some of them are knowing about what cryptocurrencies are, they unban them. Since today, all countries that accept cryptocurrencies and the ones that are very friendly with them have no problem, there banking sector has no problem. You can even see in those countries that some banks are allowed to hold coins and tokens for their customers. Banks can even embrace cryptocurrencies.
Cryptocurrency are not threats to the banking system,they are simply existing predominantly and making lasting changes in the history of economics just to promote financial stability.
The only threats that I see as a threat is that traditional banking system are scared of losing their large generation of customers in the hands of crypto assets,because they feel that they are investing huge sum of money into cryptocurrency and that way there're promoting the growth and stability of crypto assets.
With reference to information and news content drawn,a recent study by Piplsay shows that 38% of Gen X, 49% of Millennials and 13% of Gen Z own cryptocurrencies.Gen Z is relatively obsessed or connected with cryptocurrencies,that is to say banks are gradually losing their leading roles,as in an important leading role to the crypto industry.
Although it doesn't really seem like a threat,but all of these are challenges that the banks will need to face and overcome.