how do i keep your email address hidden on the proton drive

You don't. But you can create another email under your account that's not obvious (like [email protected]). I mean law enforcement would still get to your account, but some random person who got your phone wouldn't be able to identify you with it. And use it to log into the VPN app as well.

You can also protect all Proton apps (except the VPN) with pin/biometrics