Unlike Gmail, Proton Mail does a terrible job persisting preferences about the default view, specifically the preference to restrict results to Unread.

Every time I visit the website it forgets the preference.

Every time I hit the Proton Mail refresh button it forgets the preference.

Every time I relaunch the mobile app it forgets the preference.

Frankly this platform is beset by hundreds of simple UX screwups that management evidently cares not to fix. Don't use Proton use a competitor.