TL;DR: Create a new local administrator account - Log in to that account - Fix the permissions of the original account's home folder - Restart - Log in to your original account
Same thing happened to me yesterday, after installing the latest updates and restarting, logging in to my account only led to a temp account with all settings reset to default (resolution, wallpaper, icons, edge account, etc) and a popup message "We can't sign in to your account" and that I should log in and out to resolve the problem as I would lose any data created while not being properly logged in. Doing that did not help, neither did restarting the machine or booting into safe mode or trying startup repair.
As most of the steps I tried came from this article: https://support.microsoft.com/en-us/help/4027881/windows-10-we-cant-sign-in-to-your-account and I had tried them all up to moving to a new account, I decided that I had to indeed create a new account, copy my data over from my old one (that is non-system folders only) and manually change all the settings to how they were in my old account.
So I created a new administrator account after following the instructions from a link of the above article: https://support.microsoft.com/en-us/help/4026923/windows-10-create-a-local-user-or-administrator-account
After logging in to this new local administrator account and trying to access the old account's folder to move the contents, I was denied access with an error message to continue in order to gain access (it is the one that has to do with wrong security permissions/ownership of the folder).
After clicking continue and waiting for a while, the folder opened with all of the account's contents intact.
Before continuing with the transition to the newly created account, I decided to give it a shot and restart just in case it was this permissions problem causing the account not to load correctly.
After restarting the original account loaded again without any problems.
So I just deleted the newly created local administrator account and Windows is back again to how it was before.
Hope this helps!
P.S.: The problem appeared on my laptop, my desktop did not have any problems with this update.