DisplayHatMini on PiZero2W as aPocket camera

Hi guys, i need help to configure my new 2" displayhatmini on PiZero2W to work as a camera. How can I get the camera picture shown on the screen. My intention is to use X-button to get camera preview and Y-button to take picture. A and B-buttons to scan thru pictures taken. What is the simpliest way to get this function to work. I assume installing ST7789 is essential, but I dont know howto do that. So I need advice.

Okay, one step ahead, I can run examples. My OS is Buster 2021-05-07.
1: How do I get camera pisture on the screen ? Using raspistill commands .
2: How do I get Desktop on the screen ?

Its not as easy as it might seem, to get an SPI (GPIO) connected screen to become the defacto system screen. Once you get it setup driver wise, its just sitting there waiting for you to tell it what to display. All that is done over the SPI bus.
I happened on this, and saved the link. I haven’t tried it myself. See if it helps with what you want to do.
juj/fbcp-ili9341: A blazing fast display driver for SPI-based LCD displays for Raspberry Pi A, B, 2, 3, 4 and Zero (github.com)

The button actions can likely be done with some python code.