The people i know with the most simultaneous breadth and depth of knowledge just inherently enjoy learning. The skills developed are more of a side effect than the goal itself. A pattern ive seen is having some sort of an anchor in different areas, like being a professional scientist but playing regularly in a band and volunteering to coach debate. Spreading areas of focus out increases likelihood of new information being interesting and relatable to existing knowledge, which makes it faster and easier to take in, especially if it intersects with multiple areas at once.