This guide will help you find your custom lock screen wallpapers on Windows (10/11).
Open up the Windows start menu and write “Command Prompt“. (Alternatively “cmd.exe”)
Rightclick the command prompt tool and “Run as Administrator“.
In the newly opened window, write (or copy/paste):
takeown /F C:\ProgramData\Microsoft\Windows\SystemData\ /r /d Y
Press enter and close the command prompt window.
Now navigate with your “File Explorer” to:
C:\ProgramData\Microsoft\Windows\SystemData
Enter the “S-1-5-…” directory and then enter “ReadOnly“.
Here you will find your custom lock screen wallpapers in their own *“LockScreen_” **subdirectories.
Credit goes to: @Ariel and @Joe-B over at Stack Exchange. I decided to write a blog entry because it took quite some time to find this information.