I interpret Matthew 24:29-31 to be talking about Jesus's second coming in the future at the end of the age at which point the elect will be gathered to Him "in the air" (cross reference with 1 Thess 4:14-17).
Isaiah 13
6 Howl ye; for the day of the Lord is at hand; it shall come as a destruction from the Almighty.
9 Behold, the day of the Lord cometh, cruel both with wrath and fierce anger, to lay the land desolate: and he shall destroy the sinners thereof out of it.
10 For the stars of heaven and the constellations thereof shall not give their light: the sun shall be darkened in his going forth, and the moon shall not cause her light to shine.
13 Therefore I will shake the heavens, and the earth shall remove out of her place, in the wrath of the Lord of hosts, and in the day of his fierce anger.
17 Behold, I will stir up the Medes against them, which shall not regard silver; and as for gold, they shall not delight in it.
19 And Babylon, the glory of kingdoms, the beauty of the Chaldees' excellency, shall be as when God overthrew Sodom and Gomorrah.
Isaiah 34
4 And all the host of heaven shall be dissolved, and the heavens shall be rolled together as a scroll: and all their host shall fall down, as the leaf falleth off from the vine, and as a falling fig from the fig tree.
5 For my sword shall be bathed in heaven: behold, it shall come down upon Idumea, and upon the people of my curse, to judgment.
Ezekiel 32
7 And when I shall put thee out, I will cover the heaven, and make the stars thereof dark; I will cover the sun with a cloud, and the moon shall not give her light.
8 All the bright lights of heaven will I make dark over thee, and set darkness upon thy land, saith the Lord God.
15 When I shall make the land of Egypt desolate, and the country shall be destitute of that whereof it was full, when I shall smite all them that dwell therein, then shall they know that I am the Lord.
Acts 2
16 But this is that which was spoken by the prophet Joel;
19 And I will shew wonders in heaven above, and signs in the earth beneath; blood, and fire, and vapour of smoke:
20 The sun shall be turned into darkness, and the moon into blood, before the great and notable day of the Lord come.
None of the preceding passages is about the Second Coming.
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Matthew 24
29 Immediately after the tribulation of those days shall the sun be darkened, and the moon shall not give her light, and the stars shall fall from heaven, and the powers of the heavens shall be shaken:
The metaphors in Matthew 24:29 are identical or similar to those in the other passages.
None of the other passages is about the Second Coming.
Why is Matthew 24:29 necessarily about the Second Coming?