Keep track of what you spend on groceries. Probably not the first and not the overclocked budget tracking app, but a simple one that covers the essential functionality that you really need. You just put in what items you have bought, how many and the price. The dashboard shows you how much money you have spend each month.
Written in SwiftUI, the app looks and feels like your native phone apps that you are used to - and best of all: no ads ever and totally free. Spend your money on groceries, not in-app purchases or subscriptions. Happy shopping and happy tracking!