Unclear if that feature has been asked for before, the search for "stacked" was negative so far "group" not exactly what I would be suggesting.

Using the Proton client coming from Apple mail my colleagues and I struggle with (unfortunately often) large email threads with clients. We are used to be able to see grouped emails as expandable stacks being able to go directly to an email in within the stack from the overview list. Sorted from current to oldest top-down.

Currently in proton in the (left side) list it only shows the number of emails grouped together, making it necessary to scroll down in the details (right side). Also showing (fact that there are attachments) in said list view would make it easier to find the one email that may carry an important attachment while the others just talk about that one.

hope to have described that so it can be understood - discussions welcome ;)