iOS 11 split screen doesn’t work on iPad mini?
A1474 is a first-generation iPad Air, not an iPad mini.

The first generation iPads do not support Split View.


  You can use Split View with iPad Pro, iPad (5th generation), iPad Air 2, or iPad mini 4.


Use two apps at the same time with Split View - Use Multitasking on your iPad

Slide Over is supported on the first generation iPad Air, but not first generation iPad mini, once again reinforcing that you have an iPad Air and not an iPad mini.


  You can use Slide Over with iPad Pro, iPad (5th generation), iPad Air and later, or iPad mini 2 and later.


Open a second app with Slide Over - Use Multitasking on your iPad