However, Codecademy Discuss features
Categories on the left side, with topics for each category on the right side.
Moving into any given category shows this repeated, down one level. Subcategories on the left, topics for each category on the right side, with all discussion topics at the bottom.
Is the Codecademy layout a standard, built-in format for a Discourse installation? Or does this setup require a lot of custom work?
discuss.codeacademy.com uses the “Categories with featured topics” layout. You can switch to it by changing the desktop category page style site setting.
Enabling this setting doesn’t seem to enable the same layout one level down. I.e., when I click into a category, I only see the latest topics, not subcategories with featured topics. Is this something I would have to customize myself?
Correct, the above setting applies only to the main categories page. You need to configure the layout for each category, check out the settings tab within a category edit modal: