Where do I go from here?

Question

I'm almost done with the C++ course on Sololearn. It's been over a month I started and I'm already getting used to the basics of c++.
I don't want to started learning another language yet. I want to get ground in c++, I want to get baptised in it, but I guess sololearn is not the place to do that.
Any experienced programmer here? I need suggestions on places I could learn more, practice more, take coding test, exercises, quizzes, coding competitions,...
I need a place where I can read source codes of experienced developers.
Your suggestions will be greatly appreciated 🙏