I have worked on large code-bases and have built apps from scratch.
In my last company, the mobile team built the app in Swift, where we all had a hand in every aspect.
I built the registration and deposit/withdraw flows along with other aspects, such as implementing Cocoapods (e.g Flurry, Firebase) Networking, using Core Data for local DB and more.
I also have an app on the store for counting down the days to an event.