It’s the same engine, but the focus is different: CK is about the ruling dynasty, EU is about the country itself. Time period is also different (EU4 goes from 1444 to 1821),
A good example of that is that in EU4 your country can be the junior partner of a personal union, where it needs to fight against its rulers to get independence. You won’t see anything similar in CK3, because you are the ruling dynasty.