Code to populate the Card Style field

card_grid_style.php

<?php
/**
 * Get all layouts with the "Card Layout:" prefix
 */
function get_card_layouts() {
	$card_layouts = array_filter(acf_get_field_groups(), function($group) {
		return strpos($group['title'], 'Card Layout:') === 0;
	});

	return array_values($card_layouts);
}

/**
 * Get all layouts with the "Card Layout:" prefix, but
 * in an array with cleaned up labels ready for the Card Grid
 */
function get_card_layouts_as_select_options() {
	return array_reduce(get_card_layouts(), function($choices, $layout) {
		$key = str_replace('group_', '', $layout['key']);

		return array_merge($choices, [
			$key => str_replace('Card Layout: ', '', $layout['title']),
		]);
	}, []);
}

/**
 * Wire up the Card Grid style choices to get_card_layouts()
 */
add_filter('acf/load_field/key=field_card_grid_style', function($field) {
	return array_merge($field, [
		'choices' => get_card_layouts_as_select_options(),
	]);
});