I heavily use this feature in Gmail. It allows me, for example, select all the unstarred mails in the view and archive them in two clicks. With ProtonMail I have to manually archive one after another, so I won't remove important mail from the view. That's exhausting.
Folders does not help here either, because if I move some e-mails to a folder, I will remove them from the general view. That ruins the whole point of starred messages.

Miss this feature very much.

To me this is a major missing feature.
I don't see how "starred emails" are usefull without it :
This is a feature of Inbox thatI would like in protonMail :
Mark an email to process later, and be sure I will remember it, because it will be shown at the top of my inbox.