Add Media File Size Column

add_filter( 'manage_upload_columns', function ( $columns ) {

	$columns ['file_size'] = esc_html__( 'File size' );

	return $columns;

} );

add_action( 'manage_media_custom_column', function ( $column_name, $media_item ) {

	if ( 'file_size' !== $column_name || ! wp_attachment_is_image( $media_item ) ) {

		return;

	}

	$filesize = size_format( filesize( get_attached_file( $media_item ) ), 2 );

	echo esc_html( $filesize );

}, 10, 2 );