As a freelance engineer, not knowing how to efficiently invest my time in learning something new. In other words: how do I keep staying relevant in the market?

As a freelance engineer, not knowing how to efficiently invest my time in learning something new. In other words: how do I keep staying relevant in the market? Unlike other professions, having more experience does not relate to being more valued, often the opposite (image a medical doctor being dismissed for having too much experience). A software engineer (that wants to stay a developer) needs to re-invent herself multiple times during a career. How do I pick what to learn? Just going by what interests me or what is hyped doesn't seem to be a good strategy I'm working myself on a start-up to solve this problem (broad idea is to find companies that sponsor learning)