https://wccftech.com/ios-12-5-4-and-ipados-12-5-4-security-update-released-for-older-iphones-and-ipads/

Apple has released iOS 12.5.4 and iPadOS 12.5.4 updates for older iPhone and iPad models, including the iPhone 6, iPhone 5s, iPad Air, more.

If you have one of the above mentioned devices, then you can go ahead and install this update right away. Keep in mind, this is not a feature-adding update, instead it focuses on security.