[NEWS] Mac App Store broken for old versions of macOS

It's not clear if this is a temporary problem or a permananent one. One reason why having apps only downloadable from one source is a problem for those of us still using perfectly working older devices - it's just another part of enforced obsolescence by tech companies.  :-(
    Apple breaks the Mac App Store for macOS Sierra users
    -----------------------------------------------------
    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.
    While 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.
    The issue appears to have followed Apple's mid-January
    announcement to developers that it would be changing how
    certificates for App Store receipts are signed. This is how the
    App Store encodes a proof of purchase for apps.
    Apple has cautioned developers that it is possible that "your app
    will fail to validate the receipt," which could mean that "your
    customers may lose access to their content. The developer note
    explains how individual apps could be updated to avoid this.
    There doesn't appear to be a similar notice concerning the whole
    of the App Store. It's conceivable, then, that this is an error
    which will be addressed by Apple in an update.
    However, macOS Sierra is now close to a decade old. It was also
    a particularly significant release as it was the first to be
    branded macOS instead of OS X.
    It was in the following release, macOS High Sierra, that Apple
    made the switch to only 64-bit apps. This meant that older 32-bit
    software could no longer be used from this 2018 update or later.
    <https://appleinsider.com/articles/25/02/07/apple-breaks-the-mac-app-store-for-macos-sierra-users>