Nicolas Cole says your niche is your main focus, not a cage. You can share travel photos or book reviews, but most of your work should feed your core topic. The niche is the tip of the spear.
Chapters
Just because you niche down doesn't mean that you are not allowed to write about other stuff. If you travel somewhere and you want to post a picture of it, by all means. If you just finished reading an interesting book and you want to write about it, by all means. That's one of the big things that people— they feel like they have to choose, and you actually don't. Your niche is the starting point, it's the tip of the spear, but you can still write about other things, and you should give yourself the freedom to do that and know it's not like the whole thing's going to, like, fall apart. It's fine. It's just the majority of the things that you write should be in service of your goal.