Good point; I originally wanted to talk about the Poincaré conjecture as well, but then I realized that this would make the post even longer. Do you have some ideas about other interesting topics?
To be honest it's not even my field
so I know a lot less than I wish I did but yeah agreed it has no shortage of interesting things to talk about :)
Poincaré Conjecture is yeah interesting to explain though to be honest I vaguely recall an article in similar style to your post that explained it.
Possibly something like describing gradient descent on a manifold is interesting to this audience? Or maybe a post on Flatland? Many possibilities really on good follow ups.
E.g., asking for a "differentiable manifold" now asks for manifolds with enough additional structure to do calculus on top of.