A back end change to the Mac App Store appears to have shut out users of macOS Sierra and older versions, blocking not just purchases, but also downloads of software already bought.Apple's macOS Sierra came out in 2016While users of the current macOS Sequoia have recently benefited from Mac App Store changes, it's being reported that users on 2016's macOS Sierra are no longer able to use the store at all.As first spotted by blogger Michael Tsai, macOS 10.12.6 Sierra users are now just getting an error message when the attempt to sign in. It's not certain whether it is affecting all or only some macOS Sierra users, but reports are spreading on Apple support forums and social media. Continue Reading on AppleInsider | Discuss on our Forums