We use Office 365 at work and I've finally noticed two features that are critical to maintaining a clean, sane inbox: Snooze and Add to Tasks (or whatever o365 calls them -- that's Google's name for the same features).

Use cases:

Snooze: I want to come back to this email later -- get it out of my primary inbox for now; put it back in my primary inbox on [date/time]; let me view snoozed emails at any time (and un-snooze them if necessary)

Add to Tasks (requires a Task list feature): I want to turn this email thread into a Task/TODO (because I do not want to use my inbox AS a task list) -- leave it in my primary inbox, create a Task out of it (date optional); cross-link this email thread and associated Task so it's easy to go back and forth between them.

Looking at the existing feature requests, these things (or similar ideas) have been requested by numerous people for a while now, and could stand to be aggregated and prioritised accordingly:

From Proton Team, 2015 (under review since 2022, (1500+ votes):
https://protonmail.uservoice.com/forums/932842-proton-calendar/suggestions/7158378-proton-task-to-do-list

From a user, 2018 (40+ votes):
https://protonmail.uservoice.com/forums/284483-proton-mail/suggestions/36203851--postpone-email

From a user, recent (over 90 votes in first 3 months):
https://protonmail.uservoice.com/forums/945460-general-ideas/suggestions/46749442-proton-to-do-task-list

From a user, 2019 (350+ votes):
https://protonmail.uservoice.com/forums/284483-proton-mail/suggestions/36538321-snooze-feature

Some other users expressing interest in similar features:

https://protonmail.uservoice.com/forums/284483-proton-mail/suggestions/36799738-some-sort-of-due-date-reminder-or-save-for-later

https://protonmail.uservoice.com/forums/945460-general-ideas/suggestions/46795804-a-todo-type-of-app

https://protonmail.uservoice.com/forums/945460-general-ideas/suggestions/45553966-add-a-function-to-put-a-mail-on-hold-until-en-conf

I think these two features should be considered standard equipment for any inbox - a list of incoming messages is only as useful as your ability to keep them organised.

Proton folks, you had this idea yourselves about 8 years ago. If it's in the works, thank you -- if it's still being debated, please consider bumping it up a notch or two. :)