Alas, not as easy it it seems. The field itself already has the right setting. You can see this when you type something, manually delete until you’re back at the beginning and see that the shift key gets highlighted as it should.
The problem is either a bug or a feature in Apple’s implementation, not sure but when there’s a title in the field (“Untitled Note”) and we select it all, now when you delete the selected text the capitalisation isn’t triggered for some reason. I guess because the last character of the selected text isn’t a capital at the moment of the deletion the shift key isn’t active, and for some reason it doesn’t check after the deletion. @drewmccormack perhaps you know a trick to make the textfield reset to the right state.