facetwp custom image size for ACF image field in layout builder

custom-hooks.php

<?php
/**
 ** for creating custom image sizes
 ** https://developer.wordpress.org/reference/functions/add_image_size/
 **/
add_filter( 'facetwp_builder_item_value', function( $value, $item ) {
	if ( 'my-image' == $item['settings']['name'] && !empty( $value ) ) { // change 'my-image' to the unique name of your field
		$image = get_field('acf_image_field'); // change 'acf_image_field' to the name of your acf field
			if ( $image ) $value = wp_get_attachment_image( $image, 'thumbnail' ); // 'thumbnail' can be changed to other image sizes you have available
		}
	return $value;
}, 10, 2 );