Proton Mail for Web should allow marking individual contacts as "Starred" or "Favourite".

Coinciding with that, the Contacts pane should have a "Starred" or "Favourites" tab in addition to "Contacts" and "Groups".

Although this is not a critical feature, there are already at least two good reasons for it:

1. All of the extra encrypted fields in Contacts makes Proton Mail a good place not just to store your e-mail contacts, but your entire address book, including phone numbers, mailing addresses, birthdates (etc). However, this leads to the addition of many seldom-used entries that one doesn't necessarily need or want to see on the main list.

2. If "Automatically Save Contacts" is turned ON (which seems to be the default), the "Starred / Favourites" view will remain clean. I personally turned this feature OFF because I didn't want additional automatically-added Contacts entries clogging up my address book, but would have left it enabled if the feature I'm proposing existed.

In the Proton Mail for ANDROID app: if the intention is to continue showing all contacts and groups in a single consolidated list, the starred / favourite ones could simply sort to the top.