2 Answers
+ 7
No. Sololearn is not enough for ANY language on here; it is merely a starting point to learn syntax. Make some code on your own and try and test your own limits. Install Python on a desktop and try and build something advanced that you want to build (like a game). Maybe after you've made several different advanced applications/scripts in different fields could you consider yourself good at Python.
As to what to explore next, C is often recommended due to the similarities, and because it is lower level and will help you understand higher languages like Python better, so you may master it further.
+ 3
The app only touches the surface of what the language has to offer. This applies to basically all the courses that are here. Sololearn only cover the fundamentals, or what you need to know. Now since you completed the course you need to actually MAKE SOMETHING. Otherwise, it would of been for a waste. The best way of learning on how to program is to actually program. So pick a project, visit Google and find something that interests you and go from there. Good luck, and don't stop until it's done. Then look something else up.