User-defined reports are custom reports where you, as the user, can select the dimensions and metrics you want to retrieve from Google Analytics Data API.
When you select a user-defined report, you will see additional fields in the interface.
To build this type of report, you need to define the required dimensions and metrics yourself. Here is some guidance on how to do that.
How to define dimensions and metrics
Full documentation on all available dimensions and metrics in Google Analytics 4 can be found here. Additionally, we recommend using the GA4 Dimensions & Metrics Explorer tool provided by Google. By providing your Google property credentials, you can obtain a list of available dimensions and metrics specific to your account, along with linkable descriptions for all fields.
Once you have defined the required dimensions and metrics, simply provide the necessary values in the corresponding fields.