Picture says it all.
Click BTT Community to go to main page (with all the categories)
Click Setup/Preset Sharing to go to that page
This will be useful for nested subforums or 'post folders'.
My main game osu! handles their forums really well.
Click through and see how they handle their layouts. Some forums have subforums too.
AFAIK discourse doesn't support this (it's a conceptual thing because one post could be in multiple "categories").
However you can easily click the "Setup/Preset Sharing" tag in your screenshot to go back to that category, or click the BTT icon on the top left to go back to the main screen.
Thanks for the heads up! (already using that)
Maybe add the "BTT Community" label up there to make it easier to know that thats a thing you click