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.

I totally agree — starting minimal is critical for user adoption. CarPlay really nails it with its focus on essential actions.
Curious though, at what point do you think it's ‘safe’ to start introducing more complex features without overwhelming users? ￼🙃