How could we customize the all posts page in the admin panel?

Please try the code given below to add custom columns to default post type to display custom field data and make changes to the code as per your requirement.

// Add the custom columns
add_filter( 'manage_posts_columns', 'set_custom_edit_posts_columns' );
function set_custom_edit_posts_columns($columns) {
    $columns['first_field_name'] = 'Custom Field First';
    $columns['second_field_name'] = 'Custom Field Second';

    return $columns;
}

// Add the data to the custom columns
add_action( 'manage_posts_custom_column' , 'custom_posts_column', 10, 2 );
function custom_posts_column( $column, $post_id ) {

    switch ( $column ) {

        case 'first_field_name' :
            echo 'First Field Data';
            break;

        case 'second_field_name' :
            echo 'Second Field Data'; 
            break;

    }
}

Here “manage_posts_columns” is used to add the columns. You can change post type by adding custom post type name in “manage_your_post_type_name_posts_columns”. And “manage_posts_custom_column” will populate columns data. Where you can display your custom fields data. And here also you can set the post type by adding custom post type name in “manage_your_post_type_name_posts_custom_column”.

https://codex.wordpress.org/Plugin_API/Action_Reference/manage_$post_type_posts_custom_column

https://codex.wordpress.org/Plugin_API/Action_Reference/manage_posts_custom_column