So if I receive a new email, my phone notifies me, and notification stays until I open Proton Mail on my Android phone and read the email. However, if I am at home by my computer, I get a new email, my phone notifies me, but I read that email on my PC instead without touching my phone. The notification of that email stays on my phone screen until I unlock the phone and clear it.
Gmail app would clear the notification of the new email, if that email was (marked) read through PC or other device.
Why this is good idea? If I have my phone on my desk, while working with my PC, uncleared notifications of new email, which I already read on my desktop can falsely tell me that there is a new email.