That's expected. The os is getting launched only for the notification that was tapped on.
Beyond that you can use this API: https://developer.apple.com/documentation/usernotifications/unusernotificationcenter/getdeliverednotifications(completionhandler:)
to query all delivered notifications and then process those. That said I recommend against processing delivered notifications. It's not the users's intent to interact with the rest. At best you should just log them.
Like imagine if each notification caused a navigation to a certain part of your app. Do you want to process and navigate 5 notifications at once?!
Topic:
App & System Services
SubTopic:
Notifications
Tags: