This is how to create ACF rule location in product variation

acf-product-variation.php

<?php
/**
 * ACF Location Rule Product Type - Product Variation
 * Untested with repeater fields
 *
 * https://support.advancedcustomfields.com/forums/topic/custom-fields-on-woocommerce-product-variations/
 */

// Exit if accessed directly.
defined( 'ABSPATH' ) || exit;

// Check if plugin woocommerce and ACF is active
if ( ! class_exists( 'WooCommerce' ) || ! class_exists( 'ACF' ) ) return;


/**
 * Add new ACF location rule for product variation
 *
 * @param array $choices list
 * @return array $choices list
 */
add_filter( 'acf/location/rule_values/post_type', 'acf_add_rule_product_variation' );

function acf_add_rule_product_variation( $choices ) {
	$choices['product_variation'] = __('Product Variation', 'acf');
	return $choices;
}

/**
 * Render ACF fields at bottom of product variations - does not account for field group order or placement.
 *
 * @param int $loop
 * @param array $variation_data
 * @param WP_Post object $variation
 * @return void
 */
add_action( 'woocommerce_product_after_variable_attributes', 'render_acf_field_product_variation', 10, 3 );

function render_acf_field_product_variation( $loop, $variation_data, $variation ) {
	// Custom global variable to monitor index
	global $globalVariationLoop;
	$globalVariationLoop = $loop;

	// Add filter to update field name
	add_filter( 'acf/prepare_field', 'acf_prepare_field_update_field_name' );

	// Loop through all field groups
	foreach ( acf_get_field_groups() as $acf_field_group ) {
		foreach ( $acf_field_group['location'] as $group_locations ) {
			// Set rule flag
			$ruleVariationValid	= false;
			$ruleTaxonomyValid	= true;

			foreach ( $group_locations as $rule ) {
				// Check rule is product variation
				if ( $rule['param'] == 'post_type' && $rule['operator'] == '==' && $rule['value'] == 'product_variation' ) {
					$ruleVariationValid = true;
				}

				// Check rule product taxonomy
				if ( $rule['param'] == 'post_taxonomy' ) {
					$array_taxonomy = explode(':', $rule['value']);
					$taxonomy = $array_taxonomy[0];
					$term = $array_taxonomy[1];

					if ( $rule['operator'] == '==' && has_term($term, $taxonomy, $variation->post_parent) ) {
						$ruleTaxonomyValid = true;
					} else if ( $rule['operator'] == '!=' && ! has_term($term, $taxonomy, $variation->post_parent) ) {
						$ruleTaxonomyValid = true;
					} else {
						$ruleTaxonomyValid = false;
					}
				}
			}

			// Render field group
			if ( $ruleVariationValid && $ruleTaxonomyValid ) {
				acf_render_fields( $variation->ID, acf_get_fields( $acf_field_group ) );
			}
		}
	}

	// Remove filter
	remove_filter( 'acf/prepare_field', 'acf_prepare_field_update_field_name' );

	// Add ACF script for input image, gallery, etc
	echo
	"<script>
		( function($) {
			acf.do_action('append',$('.woocommerce_variation')); // For Product Block Editor
			acf.do_action('append',$('#post')); // For Product Default Editor
		} ) (jQuery);
	</script>";
}

/**
 * Filter function to update field names
 *
 * @param array $fields
 */
function acf_prepare_field_update_field_name( $fields ) {
	global $globalVariationLoop;
	$fields['name'] = preg_replace( '/^acf\[/', "acf[$globalVariationLoop][", $fields['name'] );
	return $fields;
}

/**
 * Save product variation ACF data
 *
 * @param int $variationId
 * @param int $i index
 * @return void
 */
add_action( 'woocommerce_save_product_variation', 'save_acf_product_variation', 10, 2 );

function save_acf_product_variation( $variationId, $i = -1 ) {
	// Update all fields for the current variation
	if (
		! empty( $_POST['acf'] ) &&
		is_array( $_POST['acf'] ) &&
		array_key_exists( $i, $_POST['acf'] ) &&
		is_array( ( $fields = $_POST['acf'][ $i ] ) )
	) {
		foreach ( $fields as $key => $val ) {
			update_field( $key, $val, $variationId );
		}
	}
}