If I remember correctly Promox requires the qcow2 when setting up the VM. When I set this up for a friend of mine, I followed the steps in this post: Installing Home Assistant OS using Proxmox 7 - Community Guides - Home Assistant Community (home-assistant.io)
If you dont want to use the script, then you can follow the steps outline in this post: Install Home Assistant OS in Proxmox manually (it’s not that difficult) : homeassistant (reddit.com)