If you want to start writing for a particular niche, then it is better to start researching. I am wondering how you can find the top ranking websites within a specific niche?
There are services like "The top sites" by Alexa and "Top Website Rankings" by similarweb. Do you know of any others?
If you write your keyword in the search engine, you will get the top list of websites that use the same keyword, and then you need to search for the other data from other sources. You can try to visit this page:
https://support.google.com/google-ads/answer/6337820?hl=enYou can also use Semrush Keyword Research Tool to find profitable keywords.
I heard about using software to help you find that keyword but I do not use it because it is paid software.