How to organize OneNote with chapters like a Wiki?

Question

I had to convert my Wiki page to OneNote because MS decided I need to use OneNote instead of Wiki for educational content and I noticed it removed the nav on the left. How can I get this functionality back? I don't understand why a platform so limited an unable to communicate effectively is any better with fewer tools and less ways to organize content. I bet the designers for Teams are deliberately sabotaging you, I can't fathom a reason why it's so bad, dreadfully neglected and somehow getting worse...