iCloud: "You can't sign in at this time"
Hello all, I'm hoping someone has a real solution to this. I have an older MacMini (2011) running MacOS 10.13.6 High Sierra and it has suddenly stopped letting me sign in to iCloud. I can access my iCloud via a browser but not through the Mac's system, enabling updates to Photos, Notes, Messages, Calendar, Contacts, etc.
I have googled this extensively and tried many "fixes", such as deleting ~/Library/Application Support/iCloud, deleting keychains, preferences, many, many restarts, signing in with different Mac user accounts and different iCloud accounts - all to no avail. It always ends up with getting the same message: "You can't sign in at this time".
I'm starting to think that maybe Apple have just stopped older Macs/OS versions from connecting to the iCloud - is that likely? I realise my Mac is eleven years old now (which is why it can't update beyond High Sierra) but still.
Any helpful suggestions would be most welcome. Thanks.
Mac mini, macOS 10.13
