Depends on what you're interested in, your goals and your starting point. You have two main learning lanes:

1. Theory.

Math, calculus, linear algebra, probability, statistics, ML algorithms. ISLR is a very good beginner-ish resource that helps you understand the algorithms but doesn't go too deep into the math. As you go deeper, you may realise that you have gaps in your math knowledge and you need to cover a lot more probability, calculus and linear algebra.

2. Programming.

2.1. Good software engineering practices - writing maintainable code, design patters, version control, unit testing etc.

2.2. Tooling - knowing the language-specific ecosystem of libraries (the OP is an attempt to teach you this in two languages at the same time). This is what most beginner resources focus on; your knowledge here has the least transferability and tends to go out of date quickly. Still, using the right tools and knowing them well goes a long way.