If You'll need a new app to open this windowsdefender link message appears every time you open Windows Defender, see this post.

If Windows Defender is missing and is gone or has disappeared in Windows 11/10, here are some suggestions that are sure to help you resolve the issue.

Microsoft Windows Windows 11 Microsoft's patch didn't actually fix Windows Defender, but there's a workaround News By Brendan Lowry published May 19, 2023 ...

Microsoft announced Smart App Control in April, with Weston describing it as a "major enhancement to the Windows 11 security model" designed to allow only safe and reliable apps to open.