I have bought extra iCloud storage but how do I now share this?
How can I share storage with family members on the ICLOUD family thing
also why will my Mac mini not update to OS Catalina?
Question marked as
See the following: Share an iCloud storage plan with your family - Apple Support
(and note that only 200GB and larger plans can be shared)
Is your Mac Mini a 2012 or later model? See: How to upgrade to macOS Catalina - Apple Support