Ask HN: On how many topics should a good developer focus?

I'm currently finishing my MSc in Electrical and Computer Engineering and there are many topics that excite me. However, I feel like some of them are too unrelated for me to specialize in both, like ML and OSdev, for instance. On how many of these "unrelated subjects" should one concentrate and focus on being good at? Any strategies or advice to filter the topics you should hang on to and the ones you should leave behind?