Hi Kate! This Help Center article explains how you can manage shape libraries. You'll just want to search for 'Standard' to check mark it to bring it back. Hope this helps!

Hi 

I have the same problem. 

The page you shared does not contain a solution to get the "standard" section back

Hi Maurits the article Megan linked above goes into detail on how to open the shape library manager and add shape libraries to your document. By searching for "Standard" and checking the box next to the shape library you can add it to your document.