Further to this, the Filter by Unread toggle is on the far right of the bar whereas the Sort By is on the far left.
Trivial? Maybe, but Apple have invested very heavily for decades on UI ergonomics. The Filter by Unread and Sort by Unread are two ways of achieving the same thing, finding the message(s) that is(are) flagging up in your Unread count. Filter is more efficient, so why is it not on the left with the drop down? If the columns were customisable, however, that wouldn't matter, but you then wouldn't have space for the filter button. However, in iOS Mail, the Filter button is at the fixed bottom of the scrollable area. This is where it should be in MacOS Mail as well.