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On macOS Catalina this is hidden and you have to activate it via terminal.
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(Older MacOS) Permission can be granted to open the file under: System preferences > Security & Privacy > General. The first time you do this it will not give you the option to open, but when you then repeat it then gives you the option to open the file and will add the file to a list of apps that have permission to open on your machine. It will store the file in: User Name/Library/Screen Savers/ As I am not an Apple ‘identified developer’ to enable it to work you then need to right click on the file icon and select ‘open’.
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(macOS Monterey) To install the Screen Saver automatically double click the ‘ What to do O'Clock.saver’ file and it will try and open in System Preferences and install itself automatically.
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