Run action before Ionic Vue closes or app runs in background

How can i detect in Ionic Vue if the app closes or if the app is send to the background?

this.platformor platform isn't available or does not work?!

You can subscribe to the appStateChange event, like described here: https://capacitorjs.com/docs/apis/app

Example:

import { App } from '@capacitor/app'

export default {
  created () {
    App.addListener('appStateChange', state => {
      if (!state.isActive) { // if isActive is true, App got sent to foreground, if it is false, it got sent to the background
        ...
      }
    })
  }
}