Portrait mode in Conboy focusing on reading notes? Alright, makes sense. In such case portrait mode is probably associated with one hand usage / on the go.
What about offering the notes sorted by last edited with a visible button offering to change view to last opened sorting? This would most probably satisfy use cases like shopping list, speeches, memos, classroom notes... Probably better than defaulting to alphabetical sorting. Probably that makes sense for landscape too?
[...] with a visible button offering to change view to last opened sorting [...]