Apple security updates - iOS 13

Because there are no Apple devices that are able to update to iOS 13.7. Any device that is compatible with iOS 13, is compatible with iOS 14, and will automatically update to the highest compatible version.

Because anything that can run iOS 13, can also run iOS 14. So all security updates are now only applied for iOS 14. iOS 13 has been retired and any devices that can run it, should update to iOS 14 for the most up to date files and updates.

There are however still supported devices that cannot update to iOS 13 or 14 and can only run iOS 12, so updates to iOS 12 continue to be provided for those devices as long as Apple deems it necessary.

It is very unlikely that iOS 13 will get any further updates. If you need updates for it, you go directly to iOS 14 on whatever device you have that can run iOS 13 as it can also run iOS 14.

You need to upgrade that iPad to the latest iPadOS 14.5.1 to get all the latest features and latest security updates.

Any iOS/iPadOS device that can run iOS/iPadOS 13 can upgrade to iOS/iPadOS 14.

The reason iOS 12 devices still get Apple iOS security updates is because these devices are too old and CANNOT upgrade beyond any version of iOS 12.

Your iPad is now too far behind in iPadOS upgrades/updates.

If you have access to a full computer, like a Mac or Windows PC, try either using the Finder on a Mac that has the newest macOS Catalina installed OR with an older Mac with an older Mac OS, download and install the latest iTunes version ( or latest iTunes for Windows PC ), make sure the Mac or Windows PC is connected to the Internet, connect your iPad by the USB charge cable to the computer and let the iTunes application upgrade/update thatiPad model, using the iTunes Software Update feature, to its current, maximum iOS of iPadOS 14.5.1.

Best of Luck to You!