I was also looking to see if I could submit a PR myself to fix this. I got as far as finding that clicking Undo triggers this Redux action, where the archived status is restored:

Which calls out to the setArchived action, which unpins it on archival:

But I'm not sure if there's a preferred/good pattern for remembering that status, so it can be restored when undoing, so for now I gave up there. Alternatively, maybe that action shouldn't unpin it in the first place, and the list of pinned chats should just not show archived chats. But I'm weeding into architectural decisions too much for a drive-by PR, so I'll leave t at that - but happy to take another look if so desired, if you have suggestions on where to go next.

I think for the Undo operation specifically we should also undo the unpin() that's called in conversation.setArchived. So in the onArchived() redux action we should probably save the previous isPinned state and pass that to the toast that it opens, so that when it calls onUndoArchive() it could pass the previous isPinned value in.

Perfect, thanks. PR here: #6969