I've compiled all my favourite learning platforms, courses, and books below to help guide you towards the good stuff. Everything below will help teach you how to work in the of visual language, rather than focusing on the materials (the "which iPad should I buy?" distraction).
I've read every book and taken most of the course on this page, so can at least vouch for them first-hand. But be aware it's not exhaustive. The volume of illustration education available online is constantly growing and I don't keep close tabs on it anymore.