There should be option to show sums from all subcategory payments in category (both in the Category view and in reports). Reproducible: Always
The sums are shown when the entry is shown collapsed in the categories view. Reports show the details when configured.
I just noticed that while the amounts ARE rolled up in a 5.1 Appimage (whether the Categories are collapsed OR expanded) but this does NOT happen in master branch. (I didn't check reports yet.)