New alerts in macOS 10.13.4 signal the upcoming end of 32-bit app support
Apple’s transition from 32-bit to 64-bit technology on the Mac has been in the works for a while for the company and developers, but so far users haven’t really been affected. That will start to change beginning on Thursday.
New 32-bit alerts in macOS 10.13.4 High Sierra
If you’re using an old 32-bit app on a Mac, macOS will display an alert to let you know that it may not run optimally and that you should check with the developer to see if an update is available. The alert is similar to the ones that appeared when Apple transitioned iOS from 32-bit to 64-bit.