His example of great icons from Finder is stolen directly from the Rectangle app. Looks like Apple shamelessly took Rectangle's icons.

Looking at https://rectangleapp.com/, they basically use the same idea, yes, but is there a reasonable alternative?

Also, IMO, Apple’s pictograms look a lot better and are clearer. In Rectangle, the “left half” icon almost is a dark gray rectangle alongside a bright gray one, with the _dark_ indicating where tryout window will go. In Apple’s version, there is only one rectangle and the screen border is much easier to spot.