You can blog about anything, but if you want to make money blogging, you must follow some rules. For example, you need to match your topic with keywords to be able to get readers to your blog, etc.
Another thing you’ll want to do is match your topic to available products or monetization methods. So there are some limitations.
Besides, I described this already in my article on how to make money blogging about your life which demonstrates you can really blog about anything and still be profitable.
On the other hand, if monetization is not your primary objective, then you can write on whatever you want. Your only “penalty” is that the search engines will not help you in distribution of your content and you’ll have to do this part yourself.
But if you’re more interested in business side of blogging, here’s an article on starting your side hustle from your phone.
Senior Software Developer with experience in Machine Learning, Artificial Intelligence and search engine algorithms.