You dont need a niche to start a blog. you need 1 post.
most people spend 3 weeks picking a niche and never write a word.
the niche finds you after post 10. before that youre guessing anyway. pick a topic you can write 500 words about today, not a market you think is profitable.
first post doesnt need to rank. it needs to exist. the gap between people who want to blog and people who blog is 1 published post.
WordPress, Ghost, Beehiiv — it doesnt matter. free plan, no custom domain, just get the first one out. you can migrate later. you cant migrate content that doesnt exist.
whats stopping you from publishing something today?