To-do lists, all sorts of trackers, calendar apps - the net work performed should be 0 or negative for the value it gives. Don't create work for yourself and obsess over building the perfect productivity environment.
Useful
It's a Pomodoro timer. No input needed other than starting the timer. There's just enough to make it a little more fun than a standard timer, so if a pomodoro timer works you, this is a good app.
The best productivity app. You can have other chatbots, but it creates bloat on your phone. I only pay for it when I'm using it more than the free plan allows.
Nutrition tracking. It makes tracking as easy as possible and the free version works perfectly fine. Take it from me - I am someone that will usually justify paying for the premium version of an app.
Haven't found a useful app yet
I haven't found one that provides more value than the Apple reminders app.