The new Jerusalem is completely different from Earth today.
The new Holy City, also called Jerusalem or Zion, will be a
location on the new earth as a part of the eternal heaven.
It is described as a sort of reproduction of the former dwelling
place of the Lord in the temple of Jerusalem, only this one has a throne. It won’t be a real working temple (Jesus
already completed the necessary sacrifice) but like the temple in Jerusalem
which was described as God’s home on earth or “my father’s house” by Jesus.
It descends upon the new, fully-restored, back to its original
creation, earth. The Bible says the new Jerusalem has buildings and describes
it as a real working city.
The new Jerusalem describes the place where God will dwell. Whether it's in the sky, hovering just above
the earth or directly on Earth is unclear.
The new earth will be without the old buildings and stuff that it
has now and be re-created to look like the world Adam and Eve first saw.