Ah, thank you so much for your advice! I think I misinterpreted part of the explanation for the posts array.
*Each time you make a new post, add the filepath here at the top of postsArray. This will cause all the right links to appear and work.
NOTE: It's important to follow this exact naming convention, because the scripts below are expecting it ( 'posts/YYYY-MM-DD-Title-of-Your-Post.html', ). You can alter the scripts if you want to use a different naming convention*/
I thought this meant "use a different naming convention" also applied to the "posts/" part.
I will look into your proposed solutions! Thank you so much for your time and have a nice day :)