I understand that you have restored your new iPhone X from your previous iCloud backup, but now you are unable to update the iPhone since the restore is still happening. I'm happy to provide some help for this.
Check out the information regarding this in the following article:
Get help restoring from an iCloud backup
Make sure that you're connected to Wi-Fi, because you can't restore from a backup over a cellular Internet connection. If you still need help, find out what to do based on your issue or the alert message that you see.
If a message asks for multiple Apple ID passwords
If you don't remember an Apple ID password when asked to sign in, you can tap Skip this Step and sign in later. If asked to sign in with multiple Apple IDs, it might be because your backup includes purchases that were made using more than one Apple ID. These purchases might include content like apps, movies, music, and more.
If the restore process takes a long time to finish
Stay connected to a reliable Wi-Fi network and a functional power source until the process finishes. The time it takes to restore from a backup depends on the size of your backup and the speed of your Wi-Fi network.
If a message says that your restore is incomplete or some items won't restore
These messages mean that you disconnected from Wi-Fi during the restore process or that some of your apps or content couldn't be restored. Here are some possible causes and what you can do about each:
- If a message says something like, "Restoring 350 of 1200 items," then your photos are probably still being restored. Keep your device connected to a reliable Wi-Fi network and a power outlet so that the process can finish.
- If you see a grayed-out app or one that takes a long time to load, make sure that you're connected to a Wi-Fi network. Next, tap the app to pause the process, then tap it again to continue. If this doesn’t fix the issue, delete and redownload the app.
- When your backup contains purchases that were made from more than one Apple ID, a messages asks you to sign in with multiple Apple IDs. If you can’t remember a password or didn't purchase an app using your own Apple ID account, you might see this message:
"Some apps or content can’t be restored, because they are no longer available in the iTunes or App Store, were purchased with a different account, or were synced from your computer." If you have this content saved in iTunes on your Mac or PC, try syncing your device with your computer to restore your content.
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