Hi Patrick,
Normally, upgrade will not delete your desktop data, and also reboot computer will not remove them.
To make sure if your existing user profile is corrupted or using temporary profile, we could go to C:\users to check if temp folder exists. Or we could go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList in resgitry to check if any key with .bak.
For details about repair user profile, we could refer to Windows 10 – You’ve been signed in with a temporary profile
Please note: Information posted in the given link is hosted by a third party. Microsoft does not guarantee the accuracy and effectiveness of information.
Bests,
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