Aaaaah! They are courses, not just exams or tests - then it makes sense. Thanks! I am not even going to ask what dual enrollment means

Here, students apply to university based on their final grade from high school. All high schools and programmes count the same, though some university courses require e.g. 3 years of high school physics, so if you took a HS programme that didn't include physics you would have to take those courses first. (There are a few core subjects that all HS programmes offer: Swedish, maths, history, English, but not all programmes make you eligible for university studies.) And then there is a test which is given once a year, which is open to everybody, and some proportion of the students are accepted based on that test. Of course some programmes are more popular and so the grade average required to be accepted to those is higher.

There are no high school courses that give university credits. Only students who are actually enrolled at uni can get credits. On the other hand, undergrad studies are much less tightly regulated; unless you are studying towards a particular professional degree there are no mandatory courses, and students might take undergrad courses for one semester, two semesters, fifteen semesters... they will obly get funding for something like five years I think but apart from that there's nothing to stop you from being an undergrad forever. We get a lot of retired people taking some undergrad courses.