You can also almost always switch tracks, the farther down you are one track the harder it gets to switch up. I went for the second lowest (Realschule) and then went to a tertiary school (Fachoberschule). With that I can study in a University for Applied Sciences (different from normal University).
The german education system has many options open, the general push in the lower two tracks is to get you into a job as early as possible (there are lots of job fairs I went to) but still permit you to pick any of the other 20 options.
Yet I ended up through a apprenticeship in Software Engineering and I could go back at any time and finish my 12 years then go to university. Part of me wants to go study and get a degree, but all universities I inquired at rejected me for not having 12 years despite working for 8 years now.
In Germany it's easy to be put on one of the two lower tracks which lead to apprenticeships [1], because you didn't do well in primary school. At that point is harder (but still possible) to go to college. It also leads to segregation because immigrants who don't speak German at home are unlikely to do well in primary school.
[1] Calling it blue collar is a bit of misnomer here because you can also do apprenticeships in white collar jobs, even software engineering.