Can't Install an App

Gatekeeper

macOS blocks apps that aren't from the App Store or identified developers. You'll see:

"AppName" can't be opened because it is from an unidentified developer.

Fix: Right-click the app → Open → click Open in the dialog. You only need to do this once per app.

Or: System Settings > Privacy & Security → scroll down to "AppName was blocked" → click Open Anyway.

Note: Gatekeeper is a security feature, not a bug. Only bypass it for apps you trust.

Downloaded files get a quarantine flag. If an app won't launch even after allowing it:

bash

xattr -d com.apple.quarantine /Applications/AppName.app