(1) The absolute basic "hello world" stuff at the outset. How to route URL's to their handlers, how to render dynamic templates, how to map data structures to and from JSON, etc.
(2) The problems that are one level up in sophistication, but still common to nearly all web apps. How to handle authentication (username/pass, OAuth/JWT, etc), how to manage session state or the lack thereof, juggling synchronous blocking operations with async background ones, etc.
(3) Really advanced issues that are probably specific to your industry domain or specific application, and aren't necessarily common to others (e.g. how to isolate this medical data for HIPPA compliance).
I don't want to poo-poo this website, it's nice. But in my mind, the world is already flooded with Category #1 examples. At the same time, Category #3 doesn't really lend itself to this sort of thing at all. So what the world really needs is more Category #2 stuff.
Example: What are the patterns available for authentication, including their advantages and drawbacks?
If you do your own authentication with usernames and passwords... then you have to either have to pass them every time and re-auth every request, or else store a session cookie on the client side and find some way share it across all your server-side instances (or use a load balancer with sticky sessions). That's material for 3 or 4 patterns right there!
If you use OAuth with JWT tokens, then you can (maybe) avoid the need to store any session state on the server side. But how do you explicitly "logout" prior to the JWT expiration? Another 3 or 4 patterns down this route!
Category #1 is fun and easy to write about, and a lot af that material comes from newbies who are writing in order to teach themselves. But Category #2 is the brick wall that people always run into in the real world... and because you need a lot of real experience to write about that class of problems, there's a vacuum of available material out there.