However, that application will stop working when or if you upgrade your Mac to macOS Catalina (aka macOS 10.15), which’ll be released in the fall of 2019. The application you are opening will continue to work as long as your Mac is running macOS High Sierra (aka macOS 10.13) or macOS Mojave (aka macOS 10.14). You don’t need to do anything immediately, but you need to put a plan in place. In plain English, this alert is informing you that the particular application that you’re opening, such as Word 2011, is an older application and you need to plan to upgrade to a new version. It also outlines what steps you can take, but let me try to present a clearer explanation. If one clicks the Learn More button, you’re taken to Apple’s article which offers a mildly technical explanation of the situation. This alert has generated a lot of uncertainty. Microsoft Word 2011 is only one of many applications that can trigger this alert, but Word 2011 is, by far, the most prevalent application that triggers this alert. I’ll explain what this alert means and how you should handle this situation. If you’ve upgraded your Mac to macOS High Sierra or macOS Mojave you have likely seen an alert that looks like the one shown below.