The data of Google Analytics 4 is less than that of Universal Analytics

After deploying Google Analytics 4, some people find that Google Analytics 4 has less data than Universal Analytics. The main reasons are as follows:

• Google Analytics 4 is enabled to filter Bot traffic by default, while Universal Analytics is not enabled.
• The two types of properties are using different user-identity methods, for example, the Google Analytics 4 property is using By User-ID, Google signals, then device and the Universal Analytics is using User ID—Client ID.

• Google Analytics 4 properties focus on active users (users who are currently engaged), while Universal Analytics focus on total users.