The security feature is responsible for significantly reducing the chances of malware that. By default, the Gatekeeper will not allow you to install any app, even if you trust the app developer. MacOS Catalina's Gatekeeper keeps these apps from being installed on your device for your own security.From time to time you may see the following message when Time Machine attempts to back up your Mac: Time Machine could not complete the backup This backup it too large for the backup disk.