The period selector is not a filter. It selects the period to calculate metrics for. It’s a very typical selector that works in many other apps - mostly on charts - just in Capitally there’s one that affects the whole screen to limit the confusion.
Similarly, in other apps filters act on positions, but Capitally lets you filter by open/close date, not only asset or category.
I agree the footer is confusing, but funnily enough it was introduced as a quick user-request solution with a known drawback to address later