How to Fix Windows Security Not Opening on Windows 11?
- Repair and Reset the Windows Security App
- Go to Settings.
- Select Apps.
- Go to Apps & features.
- Locate the Windows Security app.
- Click on the three dots and select Advanced option


- Hit the Repair button.
- If the issue persists, hit the Reset button.

2. Second options is to use Windows powershell.
Launch Powershell with administrator rights and run the following command:
Get-AppxPackage Microsoft.SecHealthUI -AllUsers | Reset-AppxPackage
Close Powershell and check Security working.