From Reddit. Jeez, what a convoluted mess, little of it being meaningfully implied at all by the film itself:
“Palpatine’s plan for Rey and Kylo as explained by TROS novel
Since TROS didn’t explain why Palpatine goes from “kill the girl” to “strike me down” halfway through the film, the novelization was forced to come up with some pretty convoluted explanations. Let’s take a look.
Immediately after his first death, Palpatine’s spirit enters a Clone body on Exegol (which he rediscovered during the Imperial era), but quickly realized it’s an imperfect vessel as it starts to decay. The Sith Eternal, a several thousand year old cult, creates other clones which fail until one thrives, albeit non-Force sensitive and non-identical. Realizing that he is doomed, he calls this clone his son and believes that his grandchild would inherit his force sensitivity and be able to hold his spirit. (Side Note: His Son is created in 4 ABY and Rey is born in 15 ABY, so accelerated aging is probably used on the clones).
However, his Son and Daughter in law ultimately realize his plan and hide Rey on Jakku when she is 6. Palpatine’s assassin, Ochi, can’t find her after killing her parents (genius move) and ultimately dies on his other mission, recovering the Endor wayfinder to conceal the location of Exegol. Palpatine believes Rey is dead and accepts that his going to die and decides to groom a successor to the Empire and Sith. He chooses another Skywalker and starts communicating with Ben. He also commissions the creation of Snoke to rule the First Order for him and to seduce Ben, who proves himself a worthy Sith by doing what all Sith do- kill their master. Palpatine offers Kylo his forces once they are completed making Kylo Emperor and Darth Lord of the Sith.
Even though Palpatine learned Rey is alive and he could rule through her, he decides to kill her and give Kylo everything. Once Kylo redeems himself, Palpatine contacts Pryde and has the First Order merge with his forces and decides to fall back to his original plan and possess Rey. However, she kills him and unlike in ROTJ, he wasn’t prepared to essence transfer (an art form he learned from Darth Plagueis) and dies for the last time.
There’s many problems with this. The obvious being cloning force sensitives, non-identical clones, clones not receiving midichlorians but their offspring does instead, and Ochi being a dumbass. But it’s also weird that Sidious would just be content with dying after going through all that trouble and not only that but he’s still okay with it even after learning Rey is alive. And he could sense Kylo’s redemption from across the galaxy, but he couldn’t sense his own granddaughter.”