Sure. But we can see through the atmosphere perfectly fine without any noticeable impairment when looking into space.
Effective thickness of the atmosphere (where most of the dense air is) is about 50 km.
Karman line (official Space "edge") is at 100 km.
Even directly towards horizon, the layer of the air is some 800-1000 km thick along the tangent to the Earth's surface.
From USA to Australia is 12 000 km through the most dense air.
You already saw how distant mountains slowly fade into blue sky.
Rayleigh Scattering masks the view at distances.
And at night we would need very strong city lights in Australia to see them from USA.
On the other hand, in Flat model we see stars all the way along the horizontal line to the "Dome" on the other side of the Earth.
At night it would be behind Australia.
But if you look at the Flat map, New Guinea would block the view.