Permalink structure Redirect for post only Wordpress

<?php

/**
 * custom_redirect_404_to_blog function.
 *
 * This function checks if the current page is a 404 error page.
 * If it is, it attempts to determine if the requested URL corresponds to a blog post.
 * If the URL does not already start with '/blog/' to avoid infinite redirection,
 * it checks if the requested URL, when prefixed with '/blog', corresponds to a valid blog post.
 * If so, it redirects the user to the new URI where '/blog' is prepended to the original URI.
 *
 * This code ensures that only 404 error pages corresponding to blog posts are redirected.
 * It enhances user experience by seamlessly redirecting them to the correct blog post.
 * Additionally, it prevents potential infinite redirection loops by carefully checking and modifying the requested URI.
 *
 * @since 1.0.0
 */
function custom_redirect_404_to_blog() {
    // Check if it's a 404 page
    if (is_404()) {
        // Get the requested URI without the home URL
        $requested_uri = $_SERVER['REQUEST_URI'];

        // Check if the URI does not already start with '/blog/' to avoid infinite redirection
        if (substr($requested_uri, 0, 6) !== '/blog/') {
            // Try to get the post ID based on the requested URI
            $post_id = url_to_postid('/blog' . $requested_uri);

            // Check if the post ID is for a blog post (adjust the post type accordingly)
            if ($post_id && get_post_type($post_id) === 'post') {
                // Construct the new URI by prepending '/blog' to the requested URI
                $new_uri = '/blog' . $requested_uri;

                // Perform the redirection to the new URI
                wp_redirect(home_url($new_uri), 301);
                exit;
            }
        }
    }
}
add_action('template_redirect', 'custom_redirect_404_to_blog');