I'd expect there to be some way of "only showing unread messages" (just like there is in the Desktop version of Thunderbird), but it doesn't seem to be there? "Mark as read" is there but a bit well-hidden (swipe left either on an individual message or on a thread) but "View only unread" seems to be missing? This is the case with both a personal Gmail account and a self-hosted IMAP account. In case it's relevant in the first case there is a "[Gmail]/Starred" subfolder but no "[Gmail]/Unread" one; in the second case the only subfolders are ones I have created myself.