What specifically is "overall spending"?

I see my mortgage on the Trends tab.  It is one of the pie slices, and it appears as a category in the list below the pie chart (and appears to be included in the four month bar chart).

I don't believe you have any control of the Trends tab at the category level: I think all "expense" categories for the date range selected appear there (except for Transfer Out and Cash).

You can control which accounts are used on the Trends tab: see the "include in trends" column on the Accounts tab.