I want to build a blog with react, where should I store my content?

Hey web-devs!

I own 3 WP websites, 1 built with elementor, and 2 with some other theme. All 3 of them are terribly slow, especially on mobile, mainly because of the plugins and themes that are loading each time 95% of unnecessary css and js code.

I want to built a new blog on another niche, offer maybe some services, and mainly for practice my skills, as an experiment for SEO purposes, website speed, and for adding another thing into my portfolio for future interviews.

My question to you - I don't know where to store the data.

I can store it inside the code, and render it using some component, which will decrease the number of API calls, and will probably work a lot faster.

Or - use some third party system that will store my posts, and i'll just use fetch api each time i need a specific post.

What do you think? which is better? which is faster? why? (i dont care updating the content in the code, the question is if its more efficient than storing the content itself somewhere else?)