All the latest Mac devices will have 64-bit advanced processors, and apparently, 64-bit apps will be the preferred ones. They provide faster system performance. Most of the app developers are optimizing their apps for 64-bit from 32-bit. Right now Apple displays an alert box like the one below when the user opens a 32-bit app; this is just a one-time alert to inform us.
If you are curious to see which macOS apps are 32 or 64-bit, then go to the:
Apple Menu > About This Mac > System Report > Software > Applications
In this window, you can see the list of applications you have, and there will be a column tab named “64-Bit (Intel)” here. If the value is “Yes,” then it’s optimized for 64-bit and if the value is “No,” then it’s the usual 32-bit. That’s all. Do check your Mac devices and let us know what you find.