https://www.ucg.org/bible-study-tools/bible-study-aids/you-can-understand-bible-prophecy/beyond-the-millennium#:~:text=As%20we%20read%20earlier%2C%20at,take%20place%20after%20the%20Millennium!

Now the greatest judgment of all must begin. As we read earlier, at Jesus Christ’s return only His faithful saints will be resurrected. Prophecy reveals that “the rest of the dead did not live again until the thousand years were finished” (Revelation 20:5). Another resurrection will take place after the Millennium!

The enormity of this event is difficult to convey, and its significance is hard to imagine. What is to happen to the unsaved billions of people who have ever lived? What is this time of judgment all about?

Now is the time for all other people—all those who lived from Adam’s time up to the generation living into the Millennium at Christ’s return—to learn the truth of God and enjoy the same opportunity for salvation given to those whom God called during the Millennium. They will all be raised from the dead with a marvelous opportunity to know God for the first time!

First, notice the description and setting of this resurrection: “Then I saw a great white throne and Him who sat on it …” (Revelation 20:11).

John, in vision, then witnessed an astounding sight: “And I saw the dead, small and great, standing before God, and books were opened. And another book was opened, which is the Book of Life. And the dead were judged according to their works, by the things which were written in the books” (Revelation 20:12).

This is the resurrection of the “rest of the dead” mentioned earlier. In his vision John saw them stand before God’s throne.