But... I am Jon, and I'm not familiar with any family sharing setup.
I've called Apple Support about this but they say I need to log in with the iCloud account my primary account is associated with, but I've no idea what account that could be. As far as I'm concerned I have one and only one iCloud account, and I haven't made any account changes in years. Apple Support insists they can't look up more information.
So how do I use Family Sharing in this situation? Or even just debug this? Apple Support insists there's nothing they can do so I'm not sure what to do next, anyone got any ideas??