Is the art of critical thinking practical, or theoretical? My view is that it is very definitely practical.
How is it relevant to life as an adult? Well it informs just about every decision we have to make. At least it can do, if we choose to make it so.
Earlier you have talked of learning about money matters. Critical thinking can be invaluable in that regard. Buying your first (or 21st) car? Critical thinking. Choosing between university majors? Critical thinking. Four hundred and twenty two further examples available on request.
Is critical thinking taught in schools? I am sure there are some that may have it on the curriculum, but not, I suspect, the majority. Now it may not be called critical thinking, but it is implicitly taught in any science course worthy of the name.
That being the case, why did I acquire critical thinking skills at school and yet many of my peers failed to do so? Was this the fault of the school, or a consequence of the character and circumstances of those other pupils?
What is my point? I agree that the education system in many countries, perhaps all, could be improved, but I don't accept that they are necessarily as faulty as you suggest.