Option to [show] / [show when unread] / [hide] folders and tags
[This is the same capability that exists for Gmail.]
In order to archive / classify emails I have a large number of folders and a smaller numbers of tags. This forces a lot of scrolling on the left panel of my ProtonMail when looking for unread emails, and just generally looks cluttered.
In order to make this cleaner / more efficient there should be three options for each user-created folder and tag:
1) Show (always)
2) Show (only if there is an unread message; if there are no unread messages the folder/tag defaults to "Hide" behavior)
3) Hide (always). These folders/tags would be viewable by clicking a "Show More" or "Expand" button.
Again, the user would be able to set this behavior for each user-created folder, not a uniform setting for all folders.
BONUS This behavior could also include system folders like Spam.

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Alex commented
Should this feature be implemented, I would find it more useful still if it could be expanded to "show folder only if not empty" / "hide folder if empty" - I use folders to auto-sort emails from my SimpleLogin aliases, and currently there is no way of differentiating an empty folder from a folder with only read (no unread) messages.
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Anil M commented
Good idea, I also have this particular problem and it would be great to be able to hide folders. Gmail already does this and it's very useful.