someone who knows a lot about C ++, I have a question if it is necessary to learn the entire C ++ course to develop software?

Question

C++

Answer 1

Do you mean the sololearn C++ course? Yes, you need to learn the topics and more

Answer 2

not entirely, you just need a good grasp of OOP and STL library. Then choose an API on your own and learn it's documentation to make the software.
C++ course on sololearn can only get you started.