Isaiah 40:22 It is he that sitteth upon the circle of the earth, and the inhabitants thereof are as grasshoppers; that stretcheth out the heavens as a curtain, and spreadeth them out as a tent to dwell in:
In fact let me go deeper with this idea. The Hebrew word used in this verse is חוּג or 'chug' which means vault or horizon. The definition of vault means "
a large room or chamber used for storage, especially an underground one" or "
a roof in the form of an arch or a series of arches, typical of churches and other large, formal buildings." So in this verse it either means a large cuboid 3D space or an arch that goes over the top of us, not horizontally around us or a 2D shape.
This same word is used in Proverbs 8:27 "I was there when he set the heavens in place, when he marked out the
horizon on the face of the deep," Does that mean God put a circle on the face of the deep or an arch over the top of it?
We also find the same Hebrew word in Job 22:14 "
Thick clouds veil him, so he does not see us as he goes about in the vaulted heavens" So the heavens are an arch over us?
Using the Hebrew definition of חוּג or 'chug' which is vault or horizon on Isaiah 40:22 Where does God sit then? at the edge of the earth at the horizon? no. Because it says he sits on top or above the inhabitants so he would sit on top of the vault or arch that goes over the earth. This is beginning to sound more like a sphere than a flat disc.
We can see a definition given in Gesenius' Hebrew and Chaldee Lexicon that states "
חוּג m. a circle, sphere, used of the arch or vault of the sky, Proverbs 8:27; Job 22:14 of the world, Isaiah 40:22." and as Gesenius's influence as a master of Hebrew is widespread we have no reason to doubt his translation of this word. In fact many non English Bibles translate this word as spherea, orb or globus.
Honestly it falls apart more if you take the verse literally in English. It uses the word circle, but a circle is a 2 dimensional shape. If you propose that the circle is a representation of a late earth while looking down at it, then the same could be said of a sphere from any angle. As soon as you add depth to a circle, it is no longer a circle but a cylinder, a 3D shape as represented by your flat earth models. But the sphere earth has a benefit over the flat earth because it can be represented as both a 2D and a 3D shape at the same time. If the earth was a ball or sphere and the sun was behind it all you would see is a black circle, but add light and it becomes 3 dimensional. The flat earth or cylinder can not be represented as a circle in a 3D view, any part of it that was a circle is now an ellipse or oval. So it would seem to me that this verse is more likely talking about a sphere than a disc/cylinder.
BUT, I stress this, I'm not here to prove that the earth is a sphere or convert you to my side or way of thinking. I believe what I believe and you are free to believe whatever you like, I only offer thoughts to be considered just as you would say of your own arguments. But you did ask me to defend that verse so here we are. My only point with all of this is that you cannot use this verse as undeniable proof of a flat earth because at best it could refer to either a 2D or a 3D object.