Hi @pagol
How about this one?
$image = get_field('cat_thumbnail_image', $category->taxonomy . '_' . $category->term_id );
echo '<pre>';
echo "Image field value:";
var_dump($image);
echo '</pre>';
This page should give you more idea about it: https://www.advancedcustomfields.com/resources/get-values-from-a-taxonomy-term/.
Thanks!