The API allows you to launch the user’s default app for a file type or protocol. Check out - UnityEngine.WSA.Launcher for more information.
You can also enable your app to be the default app for a file type or protocol. You can set this information in Player Settings (More settings are available in Package.appxmanifest -> Declarations)
Is something described here not working as you expect it to? It might be a Known Issue. Please check with the Issue Tracker at issuetracker.unity3d.com.
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