Question: Focus on Usability or Functionality first?

Hi IndieHackers,

I'm looking at creating my first mobile app and I was thinking about what the right initial focus should be.

Should I focus on functionality, scoping out all the features I might imagine first and then build an alpha of the rough and ready functionality OR put more emphasis on usability and making an alpha which looks and feels elegant but maybe is incomplete.

I ask this in the context of initial market testing.

To put in more practical terms, should I prepare some kind of no code proof of concept demonstrating the functionality in rough form, OR

Something more akin to high fidelity mockups of the behaviour and usability of the app?

Or is this a false choice?

Any thoughts greatly appreciated. Love to hear what type of tools for either no code app prototype or interactive mockups people might suggest too!

Thanks so much