Hi i had the same problem,
So the problem was indeed a wrong user, in my case it was the user "UpdatusUser". It was tricky because it is a hidden user.
After some research I found that this user is created by NVIDIA since version 270 on desktop computers (previous version on some laptop computer already used the "UpdatusUser").
This account executes the NVIDIA update service to update things (like drivers) through the NVIDIA's server. So it seems to be a common thing for NVIDIA updates.
But this account is the problem to Upgrade Windows 10.
So I uninstalled all NVIDIA drivers installed on my computer, mostly installed with NVIDIA GeForce Experience app. It requires a reboot after each unintall.
After that I move removed 2 weird users in User Profiles dialog in System Properties like so :
With main user (with admin privileges)
Open Properties for Computer
Advanced system settings (on the left side)
Settings for User Profiles (in the middle)
And in the list of "Profiles stored on this computer" I found a default profile + my profile with my name. But there were 2 others profiles which I did not know so I deleted them.
Then I remove the "UpdatusUser" folder found in "C:\Users\UpdatusUser"
After that I went to Start → Run → Regedit. (You can also press Windows key + R can to open the "Run" window and then type "Regedit" in it, then press enter.)
Navigate to the following registry key : HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
And remove all entry which contains a value with "UpdatusUser" in it.
After all that I did a reboot to be safe.
And I finally launched the media creation tool "MediaCreationTool2004.exe" to upgrade to Windows 10
After the installation of Windows 10 I reinstalled the NVIDIA GeForce Experience app with all drivers and everything is back to normal :)
All the best !
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