These 2 icons toggle UI state in Scrivener. It would be nice if the icons changed state visibly when pressed. (Have not used all the other icons, don’t know about them).
With some hesitation here … The Outliner icon could be more distinctive if it suggested at least 2 columns.
I don’t believe that would be a typical display model, going by Mac standards. Try using the “Mailboxes” button in Mail for an example. This hides and reveals the mailbox sidebar, but the icon itself doesn’t do anything. The presumption being: there is already ample evidence of the sidebar’s state by its presence or lack thereof.