Coinbase is the largest crypto exchange in the world, located in the US. You also have an option in Binance, but you have to make sure that you are not on a list that includes about a dozen states whose residents cannot open an account there.


You can't import private keys in Nano X, the hardware wallet doesn't work that way. Buy coins, send them in transaction to Nano X.


Forget that you don’t have to run KYC on a centralized crypto exchange, it’s a thing of the past. For such things you have to go in the direction of decentralized crypto exchanges, and since I've never used any, I can't recommend a specific name - but for information, there's a list here.