When I came on board, YNAB's mobile apps were functional, but disconnected from the main reason that people used them; namely checking your budget on the go before you spend, and adding transactions after you do.
The iPhone and Android apps were redesigned around these two specific tasks, with a high premium on speed and input efficiency. Part of the project included prototyping the animations with Framer to get them just so.
The iPad app was a totally new design, intended to be a full desktop replacement. The end result is a fast and fluid app that doesn't feel like a desktop app crammed into a smaller device.