Proof that there is a firmament above us but the better proof is the fact that the sun is right there. It's literally a ball floating above us.
As for the tiny curvature, they added it in the footage. Easily faked.
Some high altitude balloon footage. #space
https://video.nostr.build/b60ba2b3bf54660820fe9ccdad669bf0bd8101bd21df6937b46b4b2892d45c5b.mp4
Discussion
I don't think this is proof of a firmament but it does show the sun is smaller and more local than the globe claim.
The proof we are in a contained system is from the fact there is air pressure and a pressure gradient. You can't have one without the other.