One of my 4 Windows 11 Pro computers would not allow access to Windows Security.

So I tried what I thought would be an easy option and reloaded Windows 11 Pro using Media installation... keeping personal settings.

I assumed that Microsoft would reload all options/packages/utilities.... but no such luck.

I then used Windows Power Shell (admin) with command Get-AppxPackage Microsoft.SecHealthUI -AllUsers | Reset-AppxPackage.

Access to Windows Security was then restored.

I obtained my info/fix from the following link:

https://www.technipages.com/fix-windows-11-cannot-open-windows-security#:~:text=If%20you%20can't%20open,uninstall%20third%2Dparty%20security%20tools. 

Edit: the computer with the security access problem was an Intel NUC 10.