Be sure to exit System Preferences on your Mac.If someone else wants to install this, here is the whole process: Disable Gatekeeper I managed to install Guest Additions using VirtualBox version 6.1.16 on Windows 7 to share the clipboard values between the host and the guest. I think this applies to macOS 10.14 as well. To get around this security limitation, you need to disable multiple security features in order to install the package. The installation cannot be completed as normal because the OS now require packages to be digitally signed. On macOS 10.15 Catalina, Guest Additions cannot be installed by default.
