In the Netherlands, it's not included in the 'standard' curriculum but it's optional if you take 'Wiskunde D', i.e. basically what elsewhere is called 'advanced placement math' or some such. ('Wiskunde D' / 'math D' is basically a 'capita selecta' of various math topics for those who want to prepare for math-heavy/STEM university studies, whereas math A, B and C have fixed curricula and each lay a different foundation for various follow on studies. Math A has the stuff useful for (amongst others) medical studies, such as statistics but less calculus, math B is the most 'rigorous' and math C is for those who can't tell a fraction from an asymptote but since math is a required subject still need a way to pass their high school final exams).

When I was in highschool in Belgium 30 years ago, linear algebra (well, 'matrix calculations' is was called then) was part of math (depending on your electives) but I can understand why it's not taught today any more by default; there's just too much to teach, so you have to make choices. And I imagine that today they say 'we better do fewer things well than a lot with insufficient depth', which is what my experience is from how I took it 30 years ago. What's the point in doing linear algebra when it's only the purely numerical operations without teaching why or when you'd want to take a cross or dot product? And it's only a one semester course when you go to university anyway, so it's not like it's necessary to include early on or that any other high school subjects need it.