Downloading and running the Google Play Store APK on an Android 5.1.1 (Lollipop) device is possible but comes with severe limitations due to its age.

For devices running Android 5.1.1 (Lollipop) , maintaining the Google Play Store often requires manual intervention because many modern updates target Android 7.0 or higher

If you are running Android 5.1 (Lollipop), you might find that the Google Play Store has stopped updating automatically, or perhaps it was accidentally deleted. Because Android 5.1 is an older operating system, the latest version of the Play Store might not be compatible, but you still need a specific, stable version to keep your apps running.