Why the extra passwords?

When I start my MacBook Pro up and log in, I’m prompted for my password for two keychains, named Local Items and login. How can I stop this?

This happens if your Mac has two keychains it needs to open, neither of which uses your current password. This probably resulted from changing your login password, but that change not being reflected in your keychains.

When you enter your login password, it’s used for two functions: to open access as that user, and to open that user’s default keychain, the one named login. If the password used for the login keychain no longer matches that used to log in, when the Mac comes to open the user’s login keychain, it discovers that the password it has doesn’t match that for that keychain, so it will prompt you to enter the current password for that keychain.

How do I fix errors when backing up my iCloud Drive?

You can work around Time Machine errors such as this by adding your iCloud Drive to its exclusion list, via the Options… button in the System Preferences > Time Machine pane.

You can fix this using Keychain Access, in the Utilities folder. Start that app, and select your login keychain at the left of the window. In the Edit menu, use the Change Password for Keychain “login”… command, and change the password to the same password you use when logging in to your Mac.

You may need to open the Local Items keychain and copy-and-paste items from that into your login keychain so that macOS will never need to open that keychain either.

This should ensure that each time you log in to your Mac from now on, macOS can open the login keychain without any need for the separate alert, and that it can find all the information it needs there.

How do I use an APFS SSD or USB Flash drive with Sierra?

If you’ve formatted removable storage using this new file system, you can’t use it with Sierra or earlier. Share it from your High Sierra system instead.