Yup so we have that system like Slovenia too only it's a little bit earlier. You go to a level of secondary school at age 12, based on a test at age 11.
I personally got a maximum score of 550/550 on this test which gets you into 'gymnasium'. If you get below 545 you go to a middle-level education (will let you go to university of applied sciences, to become e.g. a marketing manager, teacher, physical therapist etc). Below 530 you do to the lower-level education (for lack of a better word), to train to become e.g. hairdresser or cook.
Anyway I got 550 but still went to middle-level as per a teachers' recommendation. (typical minimal effort maximum score kid). Later ended up still going to uni but it's a path with various hurdles and detours.
Frustrating in hindsight that this decision happens so early in life when you don't quite grasp the implications of educational & class differences, and at an age where the notion of becoming someone who volunteers in an animal shelter is way more interesting than to become a data scientist. As you grow up you realize the social stratification brought about by educational differences.
And then on top, indeed, you choose a certain flavor of high school. You get 2 years of general purpose stuff. Everyone gets both Physics and Math, as well as French and Art History, etc. But then the 3-4 years after, you choose one or the other. That's at age 14ish. And so even if you do gymnasium and everyone can go to uni, you're not going to be able to apply for medicine for example if you didn't do 6 years of physics in secondary school.
There's a lot of talk to change it. In fact I think Finland just removed the concept of 'subjects' altogether. Which is a radical thing to do, and takes a lot of effort and rethinking and reshaping of education. But it could be brilliant. Here they're talking about making secondary school a bit more general purpose, as the huge push for 'career planning' sessions for 12 and 16 year olds isn't enough to let them make informed decisions about what they'll be studying at age 20, and working in at age 30 or 40. Beyond that all of education is shifting away from skills, and towards competencies. So that if you teach 'self-learning', someone who spent 5 years in marketing can shift to become a programmer, if the economy changes. At least that's the general idea. It's a lot harder but competencies are definitely more valuable and important than skills (which become redundant as tech changes, e.g. being a skilled typewriter) in the long-term.