Since when is Heaven "above"?

You provided a graphic of what the Greeks thought, but you give no rough date for that. Presumably the source you used indicated how far back in Greek thinking such an idea went? You ask us to provide information on where the idea of Heaven being 'above' comes from, so it would have been helpful if you could have added a few details to the illustration in your question yourself.

As far back as the time of Noah the Bible provides written clues about this idea, so that's circa 3,000 B.C. Bear in mind, however, that the word "heaven" has layers of meaning. This is shown in God causing springs of the great deep to burst forth from below the ground to cause flooding that way, in combination with a deluge from the sky (heaven) above descending. Then there's a different meaning when (after the Flood) the tower of Babel was built. The builders wanted "a tower that reaches to the heavens". Yet this did not mean they planned to break through into the stratosphere! They wanted to disobey God's command to spread out over the whole earth. They would band together in a great city, to make a name for themselves in defiance of God in heaven. They were out to compete with God, said to dwell in heaven, and they would do that by their own earth-based ambitions to raise their fists to heaven and reject God's authority over them. This conveys the concept of an invisible 'place' that is 'above' the earth and the sky, which humans could not literally reach.

When we get to the time of the patriarch Abraham (some 2,000 years B.C.) we read of God "coming down" to examine the state of cities in the plain of Shinar. God also tells Abraham to look up into the night sky at the billions of stars there (no light pollution in those days) because God will make the so-far-childless Abraham's descendants as numerous as that. Above and below are words often used in the ancient Hebrew scriptures, with regard to earthly and heavenly matters.

King David of Israel wrote many Psalms speaking about God being in heaven as 'above' the earth, e.g. "The highest heavens belong to the Lord, but the earth he has given to man." That was circa 980 BC. His son, King Solomon, wrote a question asking whether, at death, "the spirit of man rises upwards [back to God who gave it], contrasting that with whether the spirit of animals went down into the earth. The Hebrew prophets also had dreams or visions about God on his throne in Heaven, overlooking earth. This idea continues in the Christian Greek scriptures, for example, the apostle Paul speaking about being "caught up to the third heaven". The last book of the Bible has visions of Heaven as other-worldly, and of "coming down" to earth. Therefore, the Bible consistently uses this idea of Heaven as being "above" and certainly "apart from" the realm of our material planet.

At the purely physical, non-religious, level, the word “heaven” is by its definition above us.

The first verse of the Bible is:

In the beginning God created the heavens and the earth.

and continues:

Thus God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament; and it was so. And God called the firmament Heaven.

"Firmament" is now an old word that is seldom used other than in scripture. A more modern translation avoids "firmament". It also uses the much less ambiguous word "Sky" rather than "heaven":

God made the expanse, and it separated the water which was below the expanse from the water which was above the expanse. And it was so. God called the expanse Sky.
— Jewish Publication Society

Strong’s defines the Hebrew word used here for heaven or sky as being:

from an unused root meaning to be lofty; the sky (as aloft; the dual perhaps alluding to the visible arch in which the clouds move, as well as to the higher ether where the celestial bodies revolve)

People knew that they were confined to the surface of the Earth, but they could also see and feel the atmosphere immediately above them, where birds flew and clouds rained upon them. This is the first heaven.

They could also see the Sun, Moon, stars, planets, etc., which were clearly far above the atmosphere. This is the second heaven.

People observed that while most of the lights in the second heaven circled around in fixed positions, a few of them moved independently. It was easy to imagine these planets as being alive. And as religious concepts developed, it was easy to associate these planets with individual gods. (The Romans called them Mercury, Venus, Mars, Jupiter, and Saturn.)

Having only one God, a god that created the Universe and so can't be part of it, Biblical religions rejected these sky-gods. The people still needed to visualize a home for God though, but lacked the concept of more than 3 physical dimensions. Under the Earth is obviously inappropriate (it’s dark and scary, and that’s where dead things rot), so they imagined yet another place located beyond the second heaven. It’s far more convenient and easier to visualize God’s home as yet another physical layer rather than as something completely separate from the physical universe. In 2 Corinthians 12:2, Paul refers to this place as “the third heaven”.

In some sense though, God’s Heaven can be thought of as being above us. Consider the two-dimensional image in the Question, and where you are now, looking at it from a third-dimension perspective, somewhere “above” the page or screen. Two-dimensional creatures on that surface wouldn’t be able to comprehend your third dimension, so they can only think of it as somewhere beyond or above everything else.

God’s Heaven is above the Earth's atmosphere, and above the Universe itself, but not in a three-dimensional physical sense.