Then why does Revelation 21 refer to Christ as “the lamb that was slain from the foundation of the world” if God hadn’t planned to redeem us through his death?
I am sorry you are confusing things here. Please read my post more carefully. you are making assumptions and reading more into what I said, than what I said.
The fact that God knew ahead of time He would have to redeem us through Christ’s death, does not mean His original creation was supposed to die. The fact He knew we would use free will and turn against Him doesn’t mean we weren’t orignally perfect and originally designed NOT to die. Death only came about because man sinned. Before that everything was very good and death did not exist.