Currently I am trying to find a work around to fetch data from server and update user defaults when app is forced quit. Can anyone suggest for this ?
Background fetch when app is forced quit
First, you may want to read about iOS Background Execution Limits
Force quit is considered a drastic choice by the user to say that they do not want the app to run, often because it misbehaved in some unrecoverable manner. My suggestion would be to respect that choice and not to find ways around it.
If you have to, you can use a Notification Service Extension as discussed at https://developer.apple.com/documentation/usernotifications/unnotificationserviceextension.
The Notification Service Extension will be executed for every visible push notification. So, it could serve your needs, as long as the user has not disabled the visibility of your notifications through various settings.
The service extension will not be executed for push notifications that will not be presented visually. This way, you are able to execute code in an extension and the user will be aware that this is happening.