Fix "App is damaged and can't be opened"
This error commonly occurs on macOS Sequoia, Sonoma, and Ventura when opening downloaded software that is not signed by an official Apple Developer ID. Apple Gatekeeper flags the application as "quarantined".
Remove the macOS Quarantine Attribute (xattr)
Open your Terminal (search with Cmd + Space > Terminal) and paste the following command, replacing AppName.app with your application's actual name:
sudo xattr -cr /Applications/AppName.app
Tip: You can type sudo xattr -cr (with a space) and then drag and drop the app icon from Finder directly into the Terminal window. Press Enter and enter your Mac password.
Allow Apps from Anywhere (Disable Gatekeeper)
To bring back the missing "Anywhere" security option in System Settings > Privacy & Security:
sudo spctl --master-disable
To re-enable Gatekeeper later, simply run sudo spctl --master-enable.
Re-sign Application Locally (Ad-Hoc Codesign)
If the app crashes immediately upon launch (SIGKILL / invalid signature), you can apply an ad-hoc local signature:
sudo codesign --force --deep --sign - /Applications/AppName.app