The federal funds rate is what banks charge each other for overnight reserves, inside a range the Federal Reserve sets. A mortgage is a long loan to a household, priced by a lender, often with the thirty-year Treasury and the lender's own spread somewhere in the conversation.
They move in public together often enough that people treat them as the same knob. They are not. The committee can cut the overnight range and a mortgage offer can sit still, or rise, because the long yield did something else that day.