check for app updates both the apps you listed have been updated for iphone x
alot of apps have not been and you will have the bars until they are
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It's up the App Developers to update their apps to work on iPhone X. If Snapchat and Instagram haven't updated their apps to cover the entire screen there's nothing Apple can do. You can certainly reach out to the app developers and ask what if any future plans they have to better utilize the iPhone X screen.
Question: iphone x not covering full screen