Possible to expand topics under categories?

Our users would like to be able to see a list of posted topic titles in each category without having to click into the category. The mobile view actually appears to do something similar to this. At present on desktop, if you want to see everything posted in a category, you have to dive into that category. Below is a screen shot of their existing forums we’re migrating away from, with names/topic titles blanked out because it’s a very private forum, but I think you get the idea. Is there an existing theme to do this? Any thoughts on how it might be done?