Your thoughts on where to store private keys for certain software?

My client has a software which can de-and encrypt their drives. In order to de- and encrypt they need a private key and a password.

From my point of view it may be better to store they key somewhere else e.g a usb drive but not on the system itself. The client does not understand this. They say you still need a password to login. What would you say?

cybersecurity keys software store