1060 At the end of time, the Kingdom of God will come in its fullness. Then the just will reign with Christ for ever, glorified in body and soul, and the material universe itself will be transformed. God will then be “all in all” (1 Cor 15:28), in eternal life.
Will the just be reigning with Christ in heaven or on earth?
Is there a difference between heaven and earth in the reign of Christ after the end times?
We have few details, but Heaven isn’t a separate mystical realm such that it’s Earth or Heaven. It’s not a physical place. Heaven and Earth become one, in the sense that the Earth will be remade and filled with God’s presence. We will have bodies and be on Earth, but we’ll also have the Beatific Vision of God. Or so I understand it.
Heaven is the Beatific Vision. Anywhere we experience the Beatific Vision is Heaven. After the Resurrection, we will experience the Beatific Vision in our physical natures on Earth. As such, the answer is both.
Prior to the Resurrection, Heaven will be a purely spiritual reality which only our souls will experience. After the Resurrection, we will be reunited with our bodies, and will experience the Beatific Vision both physically and spiritually.