Apple has recently begun warning users about 32-bit application compatibility. These applications are relics — although some are still in heavy use without a development team to support or update them — and will one day be phased out for the 64-bit versions most developers have been spitting out for at least half a decade.
Just because an app is currently 32-bit doesn’t mean the developer won’t get it ready by the time macOS requires it. Many apps will only require a re-compile.
When I reviewed my list, the app that gives me the greatest cause for concern is Clarify, a great app for annotating images and creating tutorials. The app is no longer sold and is in maintenance mode. I hope “maintenance mode” includes getting it ready for the 64-bit requirement.