Unable to edit header on posts page

I am new to wordpress and have a localhost install that I am using for practice. I have built a website using a free theme (astra) and the elementor page builder. I want to use one of the pages on the website as a Blog page. I have specified this page as the posts page in Appearance > Reading. However, when I specify this as the posts page, the theme header that was previously there disappears. When I deselect the page as the posts page it returns. With the page selected as the posts page, I have tried to edit the page header to make it more consistent with the other pages. However, none of the changes have any effect. Any ideas on why this issue might be arising and how it might be resolved? Many Thanks