Answer 1

There is a "complete" C++ course but it seems to essentially cover the same things as the Intro and Intermediate courses. It does however have a More on the Subject section with different discussions about things like vectors, stacks, bubble sort, macros etc.
https://www.sololearn.com/Course/CPlusPlus/?ref=app

Answer 2

I don't see it either.

Maybe it is in development stage or there will not be an advanced course.

But, you can learn more using different sources of information and/or visiting C++ documentation

Answer 3

You can’t beat a good book if your serious about learning C++.

There’s loads of good books and different recommendations, some very advanced, however I believe “Thinking in C++ Vol 1” by Bruce Eckel is a easy read and a good follow on from the courses