Apple’s most meaningful communication about this inexcusable failure of support were the 404 errors from its download pages.
Catalina
All about this mysterious folder and alias which appear when you upgrade to Catalina. It could contain rubbish, or vital documents.
In the last day or so, rumours have spread about the appearance of macOS Catalina 10.15 Supplemental Update […]
Do you use third-party command tools? Are you using or planning to use Catalina? This explains how 10.15 changes first run checks on those tools, and their effect on all users.
Why third-party kernel extensions may have problems working in Catalina, and whether those KEXTs will become SEXTs.
Catalina upgrade may fail to update EFI firmware correctly in some Mac models, notable iMac17,1. Check your firmware!
Seen the reports that Apple Support recommends not installing 10.15 on new Mac minis? Well, they’re just another fake.
You’re stuck using hard disks with High Sierra or later. Could enabling defragmentation on them overcome the performance problems of APFS?
Important updates if you’re running Catalina, as they add the KEXT blocker back into their checks.
Don’t rely on being able to use any Apple installer package unless it has been downloaded recently: its certificate is about to expire.
The Eclectic Light Company 