Developers have found a new class in the latest Android P Dev Preview, which sets a minimum API version. If this is not met by an app, the OS pops up a warning message stating: "This app was build for an older version of Android and may not work properly. Try checking for updates, or contact the developer." The current minimum API version set in Android P is 17, which is 4.2 Jelly Bean. We are yet to see if this will remain as a warning in the final version of Android P, or it will block apps from running. Google has already shown its dedication to bringing the Play Store...
Source: https://www.gsmarena.com/older_android_apps_may_stop_working_after_android_p-news-30149.php