I have tried to install RatOS onto my SD card multiple times. I have tried version 2.0.2 along with version 2.1.0 RC2 and neither of them seem to work. I keep getting this error.
Solution
It looks like balena does that automatically. I was using winrar to unzip it. The issue is the newer version is having issues with ratos for some reason. Try an older version, someone reported 1.18.1 worked https://github.com/balena-io/etcher/releases/tag/v1.18.11 or try the raspberry pi imager or Rufus