Please add a setting to Proton Mail’s desktop and web apps that allows users to choose when a message is marked as read:

Immediately when opened

After a configurable delay

Only when manually marked as read

I use Proton Mail Bridge with Thunderbird and have disabled Thunderbird’s automatic “Mark as read” behavior. Thunderbird correctly keeps opened messages unread, but opening one in Proton Mail immediately changes the shared read status and synchronizes that change back through Bridge.

A manual-only option would support workflows where “unread” means the message still requires attention. The existing automatic behavior could remain the default.