Try Basic Fixes
Uninstall any third-party antivirus program: Third-party antivirus programs can sometimes interfere with the Windows Security app and prevent it from opening on your Windows 11 PC. To avoid any conflicts, it’s best to disable or uninstall any third-party antivirus program.
Install Windows updates: Updates are crucial for any operating system and Windows is no exception. Aside from new features and security patches, these updates also carry important bug fixes. You can download and install any available updates and see if that resolves the issue.