In WordPress settings you can set a page as the
Posts Page. This can be found:
WP-Admin->Settings->Reading Settings->Front page displays
How do I retrieve the page ID that is set in this setting?
Below are the methods you can try. The first solution is probably the best. Try others if the first one doesn’t work. Senior developers aren’t just copying/pasting – they read the methods carefully & apply them wisely to each case.
<?php $page_for_posts = get_option( 'page_for_posts' ); ?>
This will return the ID of the Page assigned to display the Blog Posts Index.