You do not have to use a category for each post.
In fact, the file for displaying all messages of any category and date is index.php. You just write "loop" as the code says.
So, if you changed index.php to make it look like a fancy page, not just a mailing list, now you are trying to create another page for this.
So, if you follow me, you are doing it wrong. What you need to do is create a separate page and set it as the main page of your blog. Then it will free the index.php file so that you use it as a blog list, since it is by default.
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