Apple began transitioning to 64-bit hardware and software technology for Mac over a decade ago, and all modern Macs now include powerful 64-bit processors that can run advanced 64-bit apps. These apps can access dramatically more memory, enable faster system performance, and take advantage of technologies that define today's Mac experience.

1. If you need the storage space or prefer the cleanliness of only retaining apps that work, delete your 32-bit apps. But don’t feel compelled to. This Mac 911 article is in response to a question.
2. MacOS 10.14 Mojave, the version of the Mac operating system before the new macOS Catalina, is the last version that supports 32-bit software.With Catalina, only 64-bit software will be supported.

Apple has been working with developers to transition their apps, and in 2018 Apple informed them that macOS Mojave would be the last version of macOS to run 32-bit apps. Starting with macOS Catalina, 32-bit apps are no longer compatible with macOS.

Macos Catalina 32 Bit Support

If you get an alert about a 32-bit app

You will see one of these alerts when attempting to open a 32-bit app:

32-bit apps don't work as is on an unmodified OS. There's a lot of components to 32-bit support on a 64-bit OS. There's a lot of components to 32-bit support on a 64-bit OS. The question is how much of those are removed, if any, and whether it is feasible/possible at all to restore this support by modifying the system.

Macos Catalina And 32 Bit Apps

[app name] needs to be updated.
The developer of this app needs to update it to work with this version of macOS. Contact the developer for more information.

[app name] is not optimized for your Mac and needs to be updated.
This app will not work with future versions of macOS and needs to be updated to improve compatibility. Contact the developer for more information.

When installing macOS, you may see a list of recently used apps that are 32-bit. You can review this list before deciding to continue installation. You may also see a prohibitory symbol over the icon of each 32-bit app in the Finder, letting you know that the app will not open.

For all 32-bit apps, please contact the developer of the app to learn whether an updated version of their software is available or planned.