Hi @dan
Apart from all the above ML and Python resources, I would like to suggest you to get yourself enrolled in a advanced Mathematics course ( you can use platforms like Khan Academy, Brilliant, Udemy ) or start with the “Mathematics for Machine Learning” book ( Search this on Google, you’ll find it ).
I’ve read this book and it will take you through every mathematical concept with easy and concise explanations. Combining this book with 3Blue1Brown and Wikipedia will help you concrete your concepts. Also, there are other textbooks for Linear Algebra, Probability and Statistics which are the building blocks of ML.
Machine Learning is a math-heavy field. Although you can start with ML ( with a little Math ) especially with scikit-learn, you’ll need strong mathematical thinking to understand the underneath concepts and ideas. A good start will help you with advanced concepts and probably you’ll invent a new algorithm yourself!