MacRumors published a story that Apple has released an iOS and iPadOS 12.5.4 security fix for older iPhones and iPads.

Apple Releases iOS and iPadOS 12.5.4 Security Fix for Older iPhones and iPads

Apple today released new iOS and iPadOS 12.5.4 updates, with the new software aimed at older devices that are unable to run the iOS 14 update that's available on modern devices. The iOS and iPadOS 12.5.4 updates can be downloaded for free and the software is available on all eligible devices over-the-air in the Settings app. 

Apple Releases iOS and iPadOS 12.5.4 Security Fix for Older iPhones and iPads