A code to make excerpts meta box show above the post content

functions.php

<?php

add_action( 'admin_menu' , 'mytheme_remove_normal_excerpt' );

if (!function_exists('mytheme_remove_normal_excerpt')) {
    function mytheme_remove_normal_excerpt() {
        remove_meta_box( 'postexcerpt' , 'post' , 'normal' );
    }
}

add_action( 'add_meta_boxes', 'mytheme_add_excerpt_meta_box' );

if (!function_exists('mytheme_add_excerpt_meta_box')) {
    function mytheme_add_excerpt_meta_box( $post_type ) {
        if ( in_array( $post_type, array( 'post', 'page' ) ) ) {
            add_meta_box(
                'mytheme_postexcerpt',
                esc_html__( 'Excerpt', 'mytheme' ),
                'post_excerpt_meta_box',
                $post_type,
                'after_title',
                'high'
            );
        }
    }
}

add_action( 'edit_form_after_title', 'mytheme_run_after_title_meta_boxes' );

if (!function_exists('mytheme_run_after_title_meta_boxes')) {
    function mytheme_run_after_title_meta_boxes() {
        global $post, $wp_meta_boxes;
        do_meta_boxes( get_current_screen(), 'after_title', $post );
    }
}