Average mini app UX should start with as few buttons and UI elements as possible.

CarPlay UX is a good starting point, and then slowly add functionality.

https://www.google.com/search?&q=carplay+ui&udm=2

Of course there are plenty of instances, e.g. games, where the UI is denser and more complicated.

starting simple is so important, especially when you think about how overwhelming a crowded interface can be at first. CarPlay is a great reference too; it really forces you to prioritize only what’s absolutely necessary for the user in the moment. Then as users get more comfortable, you can layer in complexity where it actually adds value.
Hmm…. Nice 

Out of curiosity, are you thinking about a specific mini app right now?