It's an optional, definitely not universal thing. Not all schools offer it, and even then I get the impression that it's well less than half the students take the opportunity. The implementation is also highly school dependent, which is either totally expected or a complete surprise, given that the rest of the curriculum and tests are all national level standards.
This article paints a far rosier picture than I've really seen from the local experiences, but that's probably as much the lack of drive at the school than anything else.
My eldest's TY experience with us was great -- we took the opportunity to AirB&B around Europe, at least till Covid hit. But we were totally comfortable with dealing with the home schooling part of that for the three of them.