Without changing any settings, the main page content vanished.
Lately, only Events plugin has been tweaked, and only at subcategories level.
I am getting the old view only from this link:
Fixed it for you. Probably a caching delayed effect of me trying to fix the Calendar / Agenda menu item two days ago. Sorry about that.
If that happens ever again, here’s how the frontpage content is configured in Discourse: the first item mentioned in setting “top menu” defined what is seen on the frontpage. In your case, you want to put “Categories” there, like it is again now.