Mac App Store Hits Snag: macOS Sierra Users Left in the Lurch

Apple has inadvertently broken access to the Mac App Store for users running macOS Sierra (2016) and older versions. The issue stems from a recent backend change implemented by Apple, which is causing these users to receive an error message when attempting to sign in or use the store. While this problem appears to affect all macOS Sierra users, it has not been confirmed if it impacts every user on versions prior to macOS Sequoia (the current version as of February 2025). The issue seems to be related to a change in how certificates for App Store receipts are signed, which Apple announced to developers in mid-January. Though Apple has provided guidance to developers on how to update apps to avoid this problem, there is no official notice regarding the Mac App Store itself. It's possible that Apple will address this issue in a future software update.