Apple has begun notifying macOS users that 32-bit applications will not work on future versions of the operating system. It’s not clear when exactly Apple will phase out support completely, but in the meantime, users can expect to see one-time alerts when firing up a 32-bit app, starting with macOS High Sierra 10.13.4. This gives them time

Source: Hot Hardware – Apple Begins Notifying macOS Users That 32-bit App Support Is Ending