GA4 how to use User ID as dimension or filter

Question

Maybe I'm missing something big here but I'm lost, I have set up the user_id and it's working fine on multiple GA4 properties, I can use the User explorer and see it. But my problem is that I need to use this user_id for custom explorers or reports but can't find a way to use it.

I read tons of articles on "how to set up the user_id" but can't find some that use this data for more advanced used than just "using User explorer". Like, I need a report to see the list of downloaded file for one user_id. Or I need to see the list of user_id per country. Or some others, but I can only have access to "Signed in with user ID".

Does Google lock access to the user_id property except in their built-in User explorer ? So we cannot use it for a custom report ? Should I create a custom dimension that is the same value as the user_id ?

Answer 1

I don't think user_id is available as a dimension in the UI or via the API (just checked here https://ga-dev-tools.google/ga4/query-explorer/)

You could add it as a custom dimension but then you'll introduce issues with cardinality and thresholds in reports.

You can access the user_id at the event level via the BigQuery extract. That's the only way I know.