Do you have another machine available e.g. PC or MAC to create the image on? I always use the Libreelec USB creator linked here - downloads – LibreELEC
ATV1200 uses an Amlogic 8726MX chipset and I'm not aware of anyone offering images for those chips now. It's possible to find S905X devices on sale for $16-30 so community developers don't take much interest in older devices (and older hardware is a pain to support).