Is it possible to retrieve user's data from a GA4 property using the User Activity API (https://developers.google.com/analytics/devguides/reporting/core/v4/user-reporting)?
I have checked the documentation but have not found anything so far. Some endpoints of the v4 API explicitly display a warning saying it is not compatible with GA4, but this User API does not display such warning.
no it is not as stated at the top of the page for the Reporting api Overview there for it apply sto the full Reporting API v4.
Note: This API does not support Google Analytics 4 (GA4) properties. Please use the Google Analytics Data API to access the new reporting features for GA4 properties.
As far as i can see there is no equivalent in GA4 yet.
Note: I pinged the team to have them add the quote to the top of that page as well.