The tutorial says (“The Outliner” page):
Unless I’m missing something or misunderstand, there is no button at all on the right of the outliner footer bar.
Hello! This section should have been highlighted in red, as it is an intended feature not yet implemented. I’m guessing it was missed due to being in a Tip box. Hopefully this will be corrected in future Tutorials, and we do intend to have this feature in the final version.
Thanks for the catch!