That is the launch screen. when you open the app from the killed state then it’s launch screen will be showing first then after view controller which you show first time on app launch. You can add a launch screen via two methods.
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You need to add a launch image in assets
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Use launchScreen storyboard.
Check out these tutorials
https://useyourloaf.com/blog/using-a-launch-screen-storyboard/
https://www.appcoda.com/how-to-add-splash-screen-in-your-ios-app/