So I made Budgie Diet, which solves all of those problems. An iOS app that uses nothing but standard Apple APIs (principally HealthKit) to let users set their goals and then intelligently help them meet them by taking into account their existing data. It's completely free of charge, has no ads and no tracking, doesn't require a login, has no optional subscriptions for extra features, doesn't send data to any third party servers (user data is stored on iCloud) and doesn't have any kind of tracking component. And the code is completely open source on GitHub under the Expat licence: https://github.com/JBNorwich/BudgieSource/
I just released version 3.0 which includes a whole host of new features and upgrades, I'd be delighted if people could give it a go and give their thoughts!