In High Sierra, users started getting warnings about a 32-bit app's future incompatibility with macOS.A similar message is available in macOS Mojave , and if you open up a 32-bit app while running Mojave, you're going to see an alert letting you know
The first step is to make sure there aren't already available updates for apps that you have on your system, which you can generally do by updating through the Mac App Store for Mac App Store apps.
Apps outside of the Mac App Store use other update methods that can vary by app, but for many, you can click on the app's name in the menu bar and choose the "Check for Updates" option.
Certain media files that use older formats and codecs are also not going to be compatible with macOS after macOS Mojave due to the 64-bit transition, and you will need to convert some iMovie and Final Cut Pro X libraries.