I found it and added the steps in my Photoshop Notes:
Selecting a square brush: Choose brush tool, click the down arrow in the number box upper left corner of the screen, click on the gear symbol upper right of little box, select your brush style
OK, glad you found them. Unfortunately I can't tell what the included brush sets are because I have close to a 100 sets in my drop down list, and that is after ruthlessly culling out sets I think I'll never use. Which is why we see a lot of people asking for better brush management.
In the Options menu for the Brushes panel, there should be an option to add the "Legacy Brushes" that were included in previous versions. See screenshot.
Sandra, the new brush set up is so confusing regards the different brush sets / folders, that what I have done is remove every single set from CC2018, and start again with the legacy sets.
One of the things that has caused a lot of trouble is that CC2018 can now store tool presets inside the brush presets panel. So you are using the brush tool and like the look of the presets I have highlighted, and you suddenly find yourself with the Smudge tool or Mixer brush. It took me longer than it should have to discover that simply holding down the Ctrl (Cmd) key when selecting one of those presets, will prevent it changing to another tool.
It is so easy to move presets between folders now, it makes sense to build yourself a favourites folder or two.
If you use a lot of brush sets, then something I have been doing for years now, is to rename the sets so they list in alphabetical order with meaningful names. I don't know how it works with OSX, but with Windows, you have to make Hidden Items visible in the File Explorer view menu.
Windows
C:\Users\'Your User Name'\AppData\Roaming\Adobe\Adobe Photoshop CC 2018\Presets\Brushes\
Even an old post provides a solution. I was able to add the legacy brushes back. I was trying to brush on a mask along a straight edge, and wanted the square brush. Thanks for the tip.
Same for 2021. Those are great for cleaning up poorly rasterized clean vector shapes. I don't get why they're "Legacy" and why I have to append a whole slew of unnecessary brushes, with even a "Legacy" Set within the Legacy set!