I hope you are well today and thank you for your question.
To help you, I want to know how you have created the blog posts page.
Have you created the blog posts page using a blog page template?
Could you please share the blog posts page URL from your site so that I can help you?
You are not using a blog page template on that page but you have set that page as a posts page in your website Reading settings.
You can create a page configure it as a blog page as shown in the attached screenshot and then add content in its content area.