>These Southern singing conventions thrived because the untrained singers, who had to sing from written music, could learn how through a technique called “solfège,” to use the music-school word for it. Plainer folks called it shape notes. You know the system. You’ve heard it a thousand times.

https://en.wikipedia.org/wiki/Solf%C3%A8ge

Solfège has nothing to do with the shapes of the notes, just the naming.

https://en.wikipedia.org/wiki/Shape_note

This is shape note.

You can use the two together obviously, but they are not the same thing.