What are the differences between the two versions?
In short, a lot. Outside of the measurement model that’s being used, some of the changes center around privacy: no IP addresses will be collected or stored, data deletion will be easier, and you’ll have more data retention options with options to turn off location-specific data and ad personalization by country.
In terms of data and reports, when you compare the information available in Universal Analytics and Google Analytics 4, not too much has really changed, outside of where to find it. Some of the bigger differences here are around engagement, monetization and retention.
Google’s article on Universal Analytics versus Google Analytics 4 has a whole host of differences between the two data models.