How to set up HA on Rasp Pi headless

I’m trying to set up HA on a Raspberry Pi 4B headless using ethernet (not WiFi). I first set up RaspOS on the Pi headless according to the instructions on Tom’s Hardware. But then I didn’t know how to install HAOS. I then tried to follow the instructions in Raspberry Pi - Home Assistant. I failed to do this because I couldn’t find an ISO image for HAOS anywhere. So I tried to select the HAOS that Raspberry Pi Imager offered me, but this too failed, because it didn’t offer me the chance to customise the install so that it would run headless.
Can someone please tell me how to do this, or point me to some instructions that explain the process?

Thank you - Rowan

I don’t think you need to customize the install for it to run headless (I assume you mean without a keyboard, monitor, mouse, etc.). Just follow the instructions through to the Start Up and Access sections after you get the SD card built.

I have now succeeded in getting it working to a basic level. My initial problem was that I was trying to connect to it via SSH and a terminal emulator. I didn’t realize that I needed to connect to it via http.

Thanks for all the help that you all provided - Rowan