What's interesting is that Isaiah is describing the same concepts observed in Genesis, Exodus, and Ezekiel.
BDB: only of vault of the heavens חוּג שׁמים התהלך Job 22:14; בְּחֻקֿוֺ חוּג עלֿ תהום ׳פנ Proverbs 8:27; הישֵׁב עַלחֿוּג הארץ Isaiah 40:22.
Ellicott: (22) The circle of the earth—i.e., the vault of heaven over-arching the earth (Job 22:14; Proverbs 8:27).
Cambridge: the circle of the earth] i. e. the horizon, where earth and heaven meet (see Proverbs 8:27), “at the confines of light and darkness” (Job 26:10). The earth with its surrounding ocean is conceived as a flat disc, on which the arch of heaven comes down. The rendering “on the vault of the earth” (see Job 22:14, “vault of heaven,” the same word) is possible, though not so good.
Pulpit Commenatry: Verse 22. - It is he that sitteth upon the circle of the earth; rather, above the vault of the earth; above the vault of sky which seems to arch over the earth. As grasshoppers; i.e. minute, scarcely visible (comp. Numbers 13:33). That stretcheth out the heavens as a curtain. So in Psalm 104:2, only that here the "curtain" is represented as one of thin gauze. The idea is common to Isaiah with Job (Job 9:8), Jeremiah (Jeremiah 10:12; Jeremiah 51:15), and Zechariah (Zechariah 12:1), and is a favourite one in these later chapters (comp. Isaiah 42:5; Isaiah 44:24; Isaiah 45:12; Isaiah 51:13).
Barnes: The circle of the earth - Or rather, "above" (על ‛al) the circle of the earth. The word rendered 'circle' (חוּג chûg) denotes "a circle, sphere, or arch"; and is applied to the arch or vault of the heavens, in Proverbs 8:27; Job 22:14. The phrase 'circle,' or 'circuit of the earth,' here seems to be used in the same sense as the phrase orbis terrarum by the Latins; not as denoting a sphere, or not as implying that the earth was a globe, but that it was an extended plain surrounded by oceans and mighty waters. The globular form of the earth was then unknown; and the idea is, that God sat above this extended circuit, or circle; and that the vast earth was beneath his feet.
Which also is the same thing observed in ancient cultures:
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A flat land with a dome over it. The dome has windows or floodgates which hold back water. The stars are placed by God in the firmament. Birds fly across the face of the firmament. God's throne, or a human being are observed above the firmament etc. These are all references throughout scripture. Like a sea of glass, like crystal, frozen like ice, like sapphire. Again all referenced language straight from scripture.
It paints a very clear picture of exactly what Isaiah was describing when he described God above a canopy or tent that rested above the circle of the earth.
