http://protonmailrmez3lotccipshtkleegetolb73fuirgj7r4o4vfu7ozyd.onion/support/extended-notifications-android
Extended Notifications in the Proton Mail app allows you to override this system setting, letting you see the sender and email subject in Proton Mail notifications while maintaining the setting for all other notifications on your device. To enable Extended Notifications, open the Proton Mail app, tap the menu (hamburger) icon on the top left of the screen and go to Settings → Push Notifications → Extended Notifications .