All desktop proton apps, including mail, disk, and vpn, should be protected with a passphrase, just like on mobile devices!
Currently, your computer can be hacked, you know nothing about it, and yet your most precious things are all exposed for the want of this single, simple pin-access feature in all Proton desktop apps!
Guys, that's the basic security, isn't it? Major secure chat communicators have it - telegram has it, session has it, why Proton doesn't have it?! It's high time to implement it! I would suggest starting from proton mail and proton disk as the most critical-data from the user security standpoint.

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Proton User commented
There is an alternative idea that is somewhat similar...
https://protonmail.uservoice.com/forums/935538-accounts-payments/suggestions/43173582-different-passwords-for-mail-vpn-and-drive -
Proton User commented
Yes, it is really useful to protect your username = email address.