Moses was not resurrected at the time of the transfiguration on the Mount in Matt. ch. 17 because Christ had not yet been resurrected. Christ was the first fruits from the dead (1 Cor. 15:20, 23).
Jesus told the people during His ministry, before He died and was resurrected, that no man had seen the Father (John 1:18; 6:46).
"And no man hath ascended up to heaven, but he that came down from heaven, even the Son of man which is in heaven." (John 3:13, KJV)
So, no other man had been resurrected before Christ, and no other man had ascended into the heaven where YHWH sits on His throne before Christ had ascended. Then, Enoch and Elijah and Moses were some place else, and that some place else was the waiting area of the grave called Paradise. Remember Lazarus and the rich man and the picture Luke gave us of Hades.
22`And it came to pass, that the poor man died, and that he was carried away by the messengers to the bosom of Abraham -- and the rich man also died, and was buried;
23 and in the hades having lifted up his eyes, being in torments, he doth see Abraham afar off, and Lazarus in his bosom,...
26 and besides all these things, between us and you a great chasm is fixed, so that they who are willing to go over from hence unto you are not able, nor do they from thence to us pass through." (Luke 16:22,23,26, YLT)
All of the souls that had died from the beginning, or had been translated before Christ died and was resurrected and ascended... all those souls were still waiting in the prison of Hades when Christ died on the cross; either in the section called Abraham's Bosom / Paradise for the saved, or in the section of torment which the Greeks called Tartarus (2 Pet. 4-6).
Hades was called a prison and it had gates. Christ went into Paradise or Abraham's Bosom when He died, taking the thief with Him (Luke 23:43). Christ held the keys to those gates (Rev. 1:18). Christ went to preach to those "in prison" (1 Pet. 3:19). The logical conclusion is that Christ preached to those souls waiting in that section of Hades called Paradise where He went at His death telling them that the kingdom was at hand, just as He had told His disciples during His ministry (Matt. 4:17). I am sure He also told them that they did not have to wait much longer, that He was coming for them "shortly" (Rev. 1:1).
As Christ stated before He died that Hades would not prevail against His church (Matt. 16:18), then that gated prison holding place called Hades no longer exists. Christ's church - ecclessia, called out ones - exists, therefore Hades has not prevailed and is a thing of the past. It ceased to exist after He returned in judgment against Jerusalem in AD 70, after He used the Romans to destroy the temple (Rev. 20:14). He threw it into the lake of fire.
The judgment scene of Matt. 25 followed directly after the warnings and prophesies of the destruction of the temple in Matt. 24. He told His disciples it would take place at the same time. The separation of the sheep from the goats in Matt. 25:31-33 was part of that coming in glory, and coming in judgment. They were linked.
Most people keep wanting to put this into our future for some end-of-time apocalypse. But that is an assumption based upon false teaching of the "end" described in Daniel 12:13. As Gabriel was telling Daniel of the end of the days of Jerusalem's desolation / destruction, and as Christ linked those days of tribulation from Dan. 12:1-2 to the destruction of the temple in Matt. 24:7-15, then the judgment of that "end" day was linked to the destruction of the temple. It was future to them in their generation. It is not still future for us reading the NT scriptures 2,000 years later.
So, Christ's second coming was in that same generation (Matt. 23:26; 24:34) of the first century AD to judge those who had pierced Him (Rev. 1:7), and those who had persecuted His saints. At the same time He took all those out of the prison of Hades; the saved to go home with Him to heaven, and the damned to be cast out forever (Rev. 20:11-13).
And, that is when Moses, and Elijah, and Daniel, and all of the rest of the souls were taken out of Hades Paradise, were resurrected.... after the temple was destroyed.
Hades no longer exists. It is gone. Now, everyone is resurrected at our individual deaths; those who die in the Lord (Rev. 14:13) to be changed in the twinkling of an eye (1 Cor. 15:52) and lifted up into heaven; the condemned to be cast into outer darkness (Matt. 22:13; 2 Pet. 2:17).
So, at the time of Moses' and Elijah's appearance with Christ on the Mt of Transfiguration, Hades was still in existence. God had allowed them to appear with Christ in a vision which Peter and the other disciples witnessed. But, they had not yet been resurrected. (1)
Moses had died and was buried by God (Deu. 34:5-6). Elijah and Enoch had been lifted up into the skies (heaven) as seen by people from the earth, just as the disciples saw Christ being taken up into the clouds (sky) at His ascension. The lifting up into the heavens was an action from the eyes of men. But, because we know that no one had seen the Father before Christ's resurrection, then neither Elijah nor Enoch nor any other soul had actually been taken into the third heaven where God sits on His throne.
The English word "translated" in Heb. 11:5 is from the Greek "μετατίθημι" or 'metatithemi" (Strong's Gr. 3346), and means "to transfer, change". (2) God had changed Elijah and Enoch, and transferred them from their earthly mortal state or position into Paradise with the rest of the saved souls who were waiting for Christ's death and resurrection - the first fruits from the dead (hades).
Since that time, since AD 70 Christ judges each soul that passes from this mortal life at our death. It was always an individual judgment as prior to the cross of Christ each soul was assigned to the appropriate section of Hades: the saved to Paradise, or the condemned to the place of torment. This was always indicated in the OT by the phrase "gathered unto his people" (Gen. 25:8; 35:29; 49:33). Moses was also gathered unto his people (Num. 27:13). (3)
But, those who died before Christ's resurrection were held in Hades until the end of the desolations / destruction of Jerusalem... until AD 70. Then they were the first resurrection (Rev. 20:5-6). That there was a "first resurrection" necessarily implies other resurrections to take place after the first one. (4) (5)
1) Frequent Mistakes - Part VII: The Translation of Enoch and Elijah at ShreddingTheVeil
2) Strong's Gr. 3346 - Biblehub
3) Frequent Mistakes - Part III: The Last Day at ShreddingTheVeil
4) Frequent Mistakes - Part VI: The End of the World, or ? at ShreddingTheVeil
5) The Resurrection in Three Parts at ShreddingTheVeil
Also see the posts at my blog for the time of His coming, and the Hebraic idioms Christ used so His disciples would know when to expect Him:
The Signs of Revelation - Part I: The Time of His Coming here
The Signs of The Feasts - Part I: Christ Told The Pharisees When... here
The Signs of The Feasts - Part II: Christ Told His Disciples When... here
The Signs of The Feasts - Part III: The Thief in The Night here