Luckaly, there is a neat litle trick that can make the Gmail app display the unread mesages only. This trick is also working for the web Gmail app.
How to Show Only Unread Messages
- Open the Gmail app
- Tap on the search icon at the top
- Now type in the following text in:unread is:unbox
- You should now see only unread messages being displayed on your screen.
Also keep in mind that this is not permanent, so you will have to type in this text in the search bar every time you want to do this. Since Google saves your previous searches, all you need to do is tap on the search bar and the text should come up as a suggestion.