Best security app!!

What is the best security app

Security for what? What threat do you seek protection for?

iOS has all the needed security most users need, but security patches concentrate on the latest models and latest software. Unsupported models won’t get security updates anymore.

Most third party apps claiming security enhancements are either highly specialized or snake-oil, imho.

to download on your I phone -5 ?

iPhone 5 has been discontinued since 2013, and won’t run the current version system software (iOS 10.x vs. iOS 17.x). Modern apps are mostly not made for such old devices.