Good question. The "Latest Topics" on the main page displays posts only from the main category. When you click on the main category, it displays the "Latest Topics" from main category as well as all sub-categories:
To me, it’s done correctly right now. This is no different from any other forum that I’ve experienced using Discourse.
You want a landing page where new and unexperienced visitors have information about what they’ve come to, not a list of current topics. It would be confusing for new visitors to just jump into a list of topics without an explanation of what the site is all about.
If you want to always land at the latest topics, a bookmark of the direct URL as @jtp10181 pointed out is what I would also recommend. Personally I just navigate to commmunity.hubitat.com, tap the hamburger menu and select “Latest Topics”.