"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:"Here is the thing, I'll agree that the way some Christians cite this verse as completely proving a Round Earth and ignoring the possibility of a Flat Circle is wrong.
But the Bible critics are equally absolutist, insisting the verse can only mean a Flat Circle, and would have used "Sphere" if what we now know the actual shape of the Earth to be was what this Author (who I view as Isaiah, but to skeptics it's "Second Isaiah") intended to describe.
That of course ignores that we are dealing with a translation of an ancient language that didn't have as technically precise a vocabulary as modern English.
The word "Sphere" is never used by KJV translators for any Hebrew word. The argument can be made that a Sphere is basically a type of circle.
I've seen people argue Isaiah would have used the word translated elsewhere as ball. Ball is not a synonym for Sphere, all balls are spheres but not all spheres are balls. I would not describe the shape of The Earth or the Moon or any other astronomical body as being a ball. You could say they are shaped like a ball but you could not actually describe them as balls. The earlier Isaiah reference to a ball says it is tossed, that tells me it means something you can toss like a ball you play games with.
You can carve into a Sphere shaped object by the way. And you could carve something else into a Sphere shaped object.
The word translated "circle" in this verse is used in total only 3 times. Isaiah 40 is the only case where it is translated "circle". Job 22:14
"Thick clouds are a covering to him, that he seeth not; and he walketh in the circuit of heaven."And Proverbs 8:27
"When he prepared the heavens, I was there: when he set a compass upon the face of the depth:"Looking at these usages of the word, I've actually considered a 3rd option, maybe it doesn't mean either a flat circle or a sphere, maybe it's not describing the Earth's shape at all? Maybe it's referring to the Earth's Orbit (Circuit) around the Sun.
The grand point to me is, it doesn't mater what the Human Author thought he was describing. The Holy Spirit made sure it was not worded in a way that was incompatible with Scientific Fact.