Is it possible to learn whole entire C# course and after that making game development??????
I don't think it's that easy to learn an entire programming language, afterall it's just a myth. As I know unity is one of the reasons why C# is so much popular for game development. And I don't think C# courses cover all the skills requires to use Unity engine. You need to take extra courses on game development.
After finishing the course you will probably have a pretty good understanding of the language, however, there are much more out there for you to learn, you can start testing out what you can do with the knowledge you currently have and whenever you face an obstacle you can search for tutorials or other sources to improve your knowledge, also, many say it's not necessary but I recommend keeping notes somewhere of what you learn, and also keep links of the tutorials and articles that helped you in the past, keeping your knowledge organized somewhere helps a lot.