Is Joel 2:30 -31 talking about Matt 24:30? No
Is it talking about the 6th seal? No
Did I notice it said before the great and terrible day of the Lord? that depends because it's clear there are confusions on the broad sense of God's wrath and a narrow sense of God's wrath
Broad sense of God's wrath has a span over the tribulation, narrow sense is on a specific day.
Joel 2:10 mirrors the 6th seal,
"Before them the earth quakes, the heavens tremble, the sun and the moon grow dark, and the stars lose their brightness" (Joel 2:10). What is interesting is that this is one characteristic of the day of the Lord itself and not a description of an event that precedes the day of the Lord.
Consequently, even within the prophecy of Joel, not all cosmic-sign passages refer to events that must precede the coming wrath of God in the day of the LORD.
Further the problem you face will be handling the following in the book of Revelation which describe cosmic signs giving diminished light:
Rev. 8:12 (4th Trumpet) -- "And the fourth angel sounded, and a third of the moon and a third of the stars were smitten, so that a third of them might be darkened and the day might not shine for a third of it, and the night in the same way."
Rev. 9:1-2 (5th Trumpet) -- "And the fifth angel sounded, and I saw a star from heaven which had fallen to the earth; and the key of the bottomless pit was given to him. And he opened the bottomless pit; and smoke went up out of the pit, like the smoke of a great furnace; and the sun and the air were darkened by the smoke of the pit."
Rev. 16:8 (4th Bowl) -- "And the fourth angel poured out his bowl upon the sun; and it was given to it to scorch men with fire."
They are the same instance in Joel, Matt. , Revelation and also in Luke 21 for that matter. Otherwise you need to prove that these 4 events all happen separately and I know you can't show 4 separate events that are almost exactly alike in scripture all in the end times.
Unless of course you are saying they are different because they are described differently. Then you have a whole other problem. Because you see, if these are different events simply because a few adjectives are different, Well then Jesus Christ was crucified 4 times. All 4 accounts in the gospels of the Crucifixion are slightly different. No 2 are described exactly alike because they are being retold by different people. I say Jesus was crucified 1 time and the differences are simply because of different people describing the same thing ( which happens a lot in the bible I might add ) . Likewise, all 4 events in Joel, Matt. Luke, and revelation are all the same thing just retold by different people.
Lastly the argument about Joel and the wrath of God is just weak. The context of the chapter and the verses clearly but this in the end times and it is clearly talking about the Wrath of God. In any other setting there would be no dispute that The " Day of the Lord " in context with the end times always means the day of God's wrath. If you have never done it, might I suggest a study on the phrase " Day of the Lord " . It is a very interesting study.
Thanks for the message that touched my heart and soul
