Why can’t I open some old software CDs?

> This happens if they use an older HFS format, which is no longer supported in Catalina. A Mac running older macOS should be able to read them, otherwise check if you can download that software or its current version.

How do I change the primary contact for autofill?

> Open Contacts, select the card you want to set as ‘My Card’, then in the Card menu, use the ‘Make This My Card’ command. Next check this in Contacts, and by opening Safari’s Preferences, clicking on the AutoFill tool, then on the top Edit button.