Hello leon,
Thank you for reaching out to the Microsoft Community and I'll be glad to assist you today.
I understand you're experiencing an issue where the lock screen picture displays as a black screen when you restart or shut down your PC. You could try these suggestions below and check if it helps.
Method 1: Change/switch your lock screen wallpaper.
Change your lock screen wallpaper from Picture to Windows Spotlight to see if it fixes the issue.
• Go to settings > personalization > Lock screen > Select Windows spotlight.
• Next, ensure you have turned on the toggle that says "Show the lock screen background picture on the sign in screen". If the issue persists,
Method 2 : Run a system scan.
• Run a System Scan - System File Checker is a utility in Windows that checks for problems with files on your computer. To run it, follow these steps:
a. In the search box on the taskbar, type command prompt, right-click and "Select Run as administrator", and then select Yes.
b. Type or Paste the Command lines one by one and click enter. (Note: Each command may take a few minutes to start and complete. Do not copy-paste the commands all at once)
DISM /Online /Cleanup-Image /CheckHealth
DISM /Online /Cleanup-Image /ScanHealth
DISM /Online /Cleanup-Image /RestoreHealth
sfc /scannow
c. After you see a message that says, "Verification 100% complete," type exit and press Enter.
d. Restart your PC and check the wallpaper on your lock screen.
I hope this information helps. If you have any questions, please let me know and I will be happy to help you further.
Best regards,
Gunasekar N