Have you heard of the Khan Academy? It’s a resource for free courses, many of them at university level. Some of their courses are available in French, including math, computer science, science, and economics.
If you try any of the courses, I’d love to hear what you think about it. Some are basic, but some are more advanced.
Khan Academy | On each subject, a course and exercises completely free
You can learn everything. In all subjects and at all levels, the authors are specialists. And it’s free.