I created an app in react native for the front end, node.js in the backend and for the authentication I using firebase.
Now, I would like to track by User uid the time they each spend on the app.
I saw there was user_engagement but it is the total of all users. Firebase has multiple functions to analyse a user but is there one to track the user time ? If not how could I proceed ?
Google Analytics is not meant to track individual user behavior, but rather for analyzing user behavior in aggregate.
While you may be able to track some user behavior by setting a user ID for the analytics events, this won't show up in the dashboards and while you can find the information in the exported data (if you export to BigQuery, I'd probably skip that and instead find a baseline solution that is closer to what you need - or start by writing my own data to (for example) one of the Firebase databases.