Any QlikView app can be consumed in any browser which supports Ajax and can execute javascript, regardless the platform. It definitely can be used in mobile devices as long as they have a browser and connection to the QlikView server.
No development is required for that, but you may find that the screen size affects how the apps are displayed, so you may need to tweak your app layout.
In addition, there is a native iOS app for QlikView in the App Store that allows you to download slices of data for offline consumption as well as normal browsing through your QlikView apps.
You need a bit of setup here, other than downloading the app: https://help.qlik.com/en-US/qlikview/November2017/pdf/QlikView%20Mobile%20Client.pdf
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