Working with labels in Proton Mail is a very good way to structure the Inbox and different work streams.
I attach labels automatically when mail through a certain email address are coming in (just one of my hacks).
This helps to sort in between work and personal or related to projects.

However, getting the mails listed with a certain label does need to open the left menue in the app, scrolling down and clicking the label in the list. As I focus on a certain project during a period I would love to see the option to create custom tabs that would sit on top of the main messages window.