Currently, Exercism uses C++17. Is there a reason not to transfer to a more recent version? There is a lot going on that is worth learning. Usually, I would use the boost equivalent, but that is not really useful here, right?
The current policy is that the C++ version in the exercises is tied to the GCC compiler from the oldest supported LTS release of Ubuntu (see issue #438 on GitHub).
I think that’s because it allows the exercises to be solved on older hardware or older systems.