Returns a specified field from the parent ACF block.

get_parent_block_field.php

<?php
  /**
	 * Returns a specified ACF field from a parent block
	 * @param string $child_id The ID of the child ACF block
	 * @param string $child_name The name of the child ACF block
	 * @param string $parent_name The name of the parent ACF block
	 * @param string $field The name of the parent's custom field to return
	 * @param boolean $return_first If $field is an array, optionally return the first item. 
	 */
	function get_field_from_parent($child_id, $child_name, $parent_name, $field, $return_first = false) {
		global $post;
		$parsed_blocks = parse_blocks( $post->post_content );

		// Loop through the post content's blocks
		foreach( $parsed_blocks as $parsed_block ) {
			
			// Look for the parent block's name 			
			if( $parent_name !== $parsed_block['blockName'] )
				continue;

			// If the parent block has innerBlocks - it should ¯\_(ツ)_/¯	
			if ($parsed_block['innerBlocks']) {
				
				// Loop throught the innerBlocks
				foreach ($parsed_block['innerBlocks'] as $innerBlock) {

					// Look for our child block's name
					if( $child_name !== $innerBlock['blockName'] )
						continue;
			
					// Look for a match in the block ID of the matching child block's name
					if ($innerBlock['attrs']['id'] == $child_id) {

						// If the returned field is an array, optionally return the first item
						if (is_array($parsed_block['attrs']['data'][$field]) && $return_first) {
							return $parsed_block['attrs']['data'][$field][0];
						}
						
						// Else, return the field value
						return $parsed_block['attrs']['data'][$field];
					}
				}
			} 
		}
		return false;
	}