preparation of sd to boot balenaOS raspi4 64

What is minimally necessary to prepare a SD card to boot balenaOS on a raspi4? I have an ethernet connection (DHCP) and understood the instruction that I then need nothing further to do. The image flashed with linux tools does not boot: the screen goes grey then no signal then grey …
There is not device showing up on my modems list of devices.

what is necessary? how is it done (preferably with linux tools).

I think balenaOS is a great idea … please help me get started!

Hi. Do you have the 8GB version of the pi4?