Starting on April 12, 2018, Macs running macOS 10.13.4 will display a one-time alert when 32-bit applications are opened. This alert will appear once per user account on the Mac, when a relevant 32-bit application is opened.
When the Learn More… button in the alert window is clicked, the following Apple KBase article opens in your default web browser:
32-bit app compatibility with macOS High Sierra 10.13.4
https://support.apple.com/HT208436
For those who need to stop this alert from being displayed in their environments, I’ve built a management profile to suppress the warning. It is available on GitHub via the link below:
https://github.com/rtrouton/profiles/tree/master/Disable32BitApplicationWarning