// functions.php
function wporg_block_wrapper( $block_content, $block ) {
	if ( $block['blockName'] === 'core/paragraph' ) {
		$content = '<div class="wp-block-paragraph">';
		$content .= $block_content;
		$content .= '</div>';
		return $content;
	} elseif ( $block['blockName'] === 'core/heading' ) {
		$content = '<div class="wp-block-heading">';
		$content .= $block_content;
		$content .= '</div>';
		return $content;
	}
	return $block_content;
}

add_filter( 'render_block', 'wporg_block_wrapper', 10, 2 );