Thanks for your comment. I think choosing a topic and sticking to it is completely unnecessary here on Medium. I would just start writing about whatever you want. Then, over time, you’ll probably gravitate towards some topics naturally. For instance, I keep publishing stuff about writing even though I’ve never consciously decided to make that my priority (it wasn’t even on my radar when I started). But I keep coming back to it because I think about it a lot more than I expected to and because people seem to enjoy my take on it.
Also keep in mind that Medium is not a blog. People come to Medium to read about all sorts of stuff and it’s specifically designed so that writers can write about whatever they want. For instance, if people are interested in a particular topic (e.g. writing), they follow particular publications (e.g. The Writing Cooperative) and particular tags/topics (e.g. medium.com/tag/writing and medium.com/topic/writing). OTOH, I think people follow individual writers because they like they’re writing style, their voice, their honesty, their humor, their silly drawings, etc.
I hope that helps :-)