> Read the main textbooks of your field and read and re-read ALL relevant papers for your actual Ph.D. topic, once you've been able to identify

I'm gonna be real as someone in grad school. Basically no PhD, grad students, or professors I know read full text books. I hear these ideas a lot, and they often sound like one of those Instagram influencer diets, that's completely unreasonable if you have any constraints in your life, and it's mostly been used to gate keep "real" scientists. Be well studied and knowledgeable about your problem domain, but you have a finite lifespan, so never feel bad that you aren't "educated enough".