Apple has announced that macOS 10.14 will be the last version capable of running 32-bit applications.

As Apple finalizes its transition to all-64-bit code, Mojave and High Sierra present an alert like this when you launch a 32-bit application. While it’s not a crisis at present, you’ll need to update or upgrade those applications before you update to macOS 10.15 later this year.

Finding out which of the applications you use each day is a good idea before you upgrade to MacOS Catalina.  St Clair Software has a great little application that can scan your hard disk and list the applications that will have problems.  The application is called Go64 and best of all, its a free download.  Check it out and make sure a critical application to your workflow will not be dying in the next Mac update.