The notable fact is that there are some basic differences between Universal Analytics and GA4. The GA4 interface collects event-based data, i.e., records each webpage interaction. In contrast, the data model for UA is based on sessions (hits) or user interaction with the page. GA4 collects data and incorporates it in a more informative pattern than the Universal Analytics interface. Another prominent factor that makes GA4 reports different from UA is adding engagement metrics and removing the bounce rate of earlier UA interfaces. That explains why the UA data is not directly merged into the GA4 interface. Due to the unmatched data model of both platforms, you cannot migrate the UA data directly to the GA4 interface.