I ran into this a bit over a week ago when I upgraded. I had been running the public beta on my 2020 iPad Pro, and upgraded 2 days after 18 officially launched, but after it was pulled for bricking M4 Pros. It sounds like 18.0.1 is in progress and should be out soon, however I installed the 18.1 public beta on mine after seeing others have success with it from 17.7.
That said, my prior upgrade sat around for at least a week before I threw the beta in and there were no issues.
If you have another iOS device, you should be able to go to settings>Account Settings (the one with your Memoji)>iCloud Backup and see all backups stored in your iCloud.
“Idaho senator born in another state tells Native American congressional candidate from a tribe native to the state to “go back where you came from.”
It would have been a much wordier headline but relays a lot more pertinent information.