If you want to draw realistically, then yes you do need to learn anatomy quite intimately. You don’t “need” anatomy to create convincing humans though. All you need are shapes that look like convincing 3d forms, and you need to draw them as though they move purposefully and naturally. (Think good flour bag animation test) You can draw “humans” with varying levels of complexity and varying degrees of stylization; therefore, all you need are the forms that YOU understand and that YOU can create. You just have to make sure that you actually fully understand the form. You don’t start learning chess by simply copying GM”s games. You learn it by picking an opening as a starting point to build concepts from. If you can only imagine (manipulate/see in your mind’s eye) AND draw a cylinder, manipulate the cylinder to be closer to the anatomical form. Don’t be too worried of what a bicep actually looks like: be only worried about what YOU imagine to be a bicep.  TLDR; you learn only the anatomy that you can use. You never finish learning anatomy, so you kind of never start. Different parts of the body will appear to you when you can find a way to use them.