The reason I believe there was a canopy of water/ice is because God says Himself that He made it that way.
Genesis 1:6-8
"And God said, “Let there be a vault between the waters to separate water from water.” 7 So God made the vault and separated the water under the vault from the
water above it. And it was so. 8 God called the vault “
sky.”"
So here we have water below and water above and between the waters is sky. This means the waters above could have been frozen in the atmosphere in someway. Definitely not impossible and would explain the state of the earth pre-flood as being super lush and oxygenated. The canopy would have caused a super greenhouse effect, which would have allowed life to grow very large, which would explain why we find large creatures like dinosaurs in the ground today. Recently paleontologists have been finding blood cells in dinosaur bones, which means there is no way dinosaurs are millions of years old, but rather thousands of years old.
What argument do you have that shows the canopy didn't exist? Just curious