It would be a very useful feature to have a periodic master password reminder, for example every few months, where the user is required to enter the master password in order to avoid forgetting it.

This could be implemented by allowing the user to choose a time interval. Once the interval is reached, access via PIN or biometrics would always be delayed (e.g. by 5 seconds) until the master password has been entered at least once. The delay would continue to apply every time the user unlocks the vault, as long as the master password has not been entered.

Especially when trying to convince new users to adopt a password manager like Proton Pass, this would be beneficial. New users are often encouraged to use a strong master password (for example a Diceware passphrase), and periodically entering it would help them remember it over time.