Try this first:
Open PowerShell (Admin) and run:
Get-AppxPackage Microsoft.SecHealthUI -AllUsers | Reset-AppxPackage
This resets the Windows Security app package.
If that fails, open Settings → Apps → Installed Apps → enable Show system components, find Windows Security (SecHealthUI), and choose Repair/Reset if available.
As a last resort, run:
sfc /scannow
DISM /Online /Cleanup-Image /RestoreHealth
from an elevated Command Prompt to fix any corrupted system files.
This usually brings Windows Security back without needing a full reinstall or trip to the shop.