I use Folders to sort between two different email address at the moment, for lack of any better solution within Proton at this time.

Having my 'Primary' Folder collapsed means I cannot see that there is Mail within a subfolder, having a +1 or '+[x]' Icon on the folder next to the usual unread-mail count such as 24 [+2] or something.

This would allow me (and others that use a similar folder structure to me, Primary->Important->Utilities or something) to target the correct folders quickly instead of using the all mail folder, which may have many other emails the user does not want to look for.

I hope this is a nice and simple thing to add, thank you.