But they deliberately overlook the fact that long ago by God’s word the heavens existed and the earth was formed out of water and by water,…
That isn't a fact.
That is a claim.
One for which there is no more evidence than the claim itself.
More so, you have 2 contradictory claims, with 2 different contradictory creation accounts.
The Bible used poetry and figurative speech throughout its entirety.
Except there is no reason at all to think it is meant to be figurative.
The only people try to claim that is to have their delusional fantasy match reality.
In what world is Genesis 4 and 5 figurative?
This serves no purpose at all other than providing an allegedly histortical family tree.
So what separates us from the vacuum of space ?
You are asking the wrong question.
The question is what is causing air pressure?
We know that air pressure pushes air outwards.
So something needs to be creating that pressure.
And that something is gravity (or whatever delusional BS you want to substitute for it).
Gravity is pulling the air down, compressing the air below.
This naturally creates a pressure gradient.
This pressure gradient is measurable, with the air pressure lower as you get higher.
You can also test it out with water.
It is this pressure gradient which separates the air at sea level from the atmosphere of space.
There is no need for any solid container.