UA traditionally uses session-based measurement for its reporting, while GA4 is event-based. The changing privacy landscape is making it very difficult to track users as they travel across different platforms digitally. GA4 uses machine learning technology to fill in any missing data in order to create a single user journey linked to the same identity. Instead of the long list of predefined reports you would find in UA, GA4 users report summary cards. Each scorecard can be analyzed deeper to extract more information from it.