i too had this problem with moving users from 6th gen to 10th gen ipads. the 10th gens were on iOS 17.7, but when i did the transfer, one of the requirements it forced was to upgrade to iOS 18.0. This forced upgrade was never a problem until 18. must be a bug.
during this process it stuck and wouldn't move. i let it sit for over an hour. (tried a second ipad with same result).
the solution i found that worked on the 2 ipads that had corrupted was the following:
get a laptop with the latest 'apple devices' app.
put the laptop on a hotspot/wifi that was NOT on our corporate network.
get the ipad in 'restore/recovery' mode.
plug it into the laptop.
the 'apple devices' software sees the ipad and prompts to 'restore' or 'upgrade'. i chose 'restore'.
the 'apple devices' will download the latest iOS, unpack, get the ipad ready and push it in.
after the first ipad was successfully brought back to life i tried the second. it failed.
i restarted the laptop and the ipad. basically starting over.
success.
when i tried this same process on our corporate network it would get halfway through the restore and freeze.
even turning off antivirus didn't help. (something on the network is obviously preventing the back and forth communication with the Apple servers, but due to the rarity of the problem, simply using a hotspot to bypass the network BS is fine with me.)