This brief tutorial will show you how to run OS X applications in 32-bit mode, in certain versions of OS X/macOS.
If you’re using a OS X 10.14.5 you can no longer use the “Open in 32-bit mode” featured outlined below, but you can try the following command to launch an app in 32-bit mode:
arch -i386 /Applications/TheApp.app/Contents/MacOS/TheApp
Although OS X was 64-bit compatible in many ways prior to Snow Leopard, Snow Leopard made a big jump in 64-bit computing by re-writing most system applications, including the Finder, Mail, Safari, iCal, and iChat, in 64-bit code. This allows these programs (and others as they are re-written) to use a lot more memory than was previously possible.
The drawback is that some programs (addons, plugins etc) that interact with these 64-bit programs, often don’t work (at least until they too are re-written in 64-bit).
One way to get around this ‘problem’ is to launch the application itself in 32-bit mode, so that all of it’s 32-bit plugins and addons continue to work.
To do so, select the program in question, right-click it (ctrl-click for single mouse button folks), and select Get Info
In the Info panel, select Open in 32-bit mode. Close the Info panel and launch the program. It will now be running in 32-bit mode.
Don’t forget to remove that check-mark in order to run the program in its native 64-bit mode (once the plugins, addons or whatever it is that caused you to require it running in 32-bit mode are updated).