When I got my first iPhone (the second one they made - the one with 3G), I started looking for To Do applications that eventually sent me down the rabbit hole of the "Getting Things Done" book by David Allen.
My goodness, this really did introduce me to a new way of thinking. I still use many of the principles today, but, having stopped work to move to the homemaker role in 2017, some of it has gone by the wayside a little.
Two of the apps that really struck me back then were Things and Omnifocus. Both were good at what they did, but the Things development team seemed to have some issues at some point, and the user base fell out with them rather, despite (or perhaps partly because of) them winning some Apple design award or other.
Omnifocus it was, then, for a while, but several years ago I switched to Alarmed by Yocotville. As another app reviewer put it, the developer of this has a better understanding of time then most people will ever need.
The only criticism of it I have ever really seen is that it only shows the "next" iteration of repeating tasks, rather than having them laid out ad infinitum. The person criticising this presumably wanted to see how future iterations would affect their calendar.
I love it, and use if for all my repeating tasks.
Hope this helps. I have no connection to any of the developers mentioned; I am just a happy Alarmed customer.