For a DIY site owner no. But if you want to go deeper you must know
- plugin dev
- post types dev
- maybe blocks dev (reactJS)
- themes dev
Also, you have to learn
- HTML
- CSS
- JS
- MySQL (relational databases)
- Colour theory (if you create Themes, User Interfaces)
- PHPMyAdmin, Xampp e.t.c.
- and more