Experienced Developer Seeking Apprenticeship

I am not looking for a job per se or looking for a salary. I am looking for some sort of apprenticeship where I can work on some tough problem in distributed systems, operating systems, or Machine learning under some guidance. Would appreciate apprenticeship on functional programming too. I am on a career break learning the above things, but I lack the confidence to contribute to open source. And have no projects that I can work on. I am an experienced developer with mostly mobile development experience. Comfortable with C++, JS, Swift, Kotlin, TS. I am a quick learner.