i'm having similar issue...
received iPhone 13 pro max yesterday.
began iCloud+ backup of iPhone X around 4pm yesterday and backup completed by the time I woke up this morning.
this morning around 8am, i started restoring to my iPhone 13 via iCloud+. it's been over 12 hours now and still says "Restore in Progress. an estimated 45.3GB will be required to finish restoring your apps and data." in settings.
Just above that, there's "Update Apple ID Setttings ..... (1)" and when i click "continue" and enter apple ID password, everything's greyed out and i have to force close settings app.
not sure if "update apple ID settings" is halting the restore or if i just need to let it restore until tomorrow morning.
home wifi upload speed is super slow but download speed is much faster. thus restore should be faster than backup, no?
because it does not show how much has been restored so far, i really don't know if it's stuck/froze or still restoring properly.