Thanks, i forgot to show my final solution to eliminate all css load by the_flexible() function:
function layout_get($content): void {
foreach ($contenus as $layout) {
foreach ($layout['layouts'] as $value) {
$handle = acf_slugify($layout['name']) . '-layout-' . acf_slugify($value['name']);
// prevent acf automatic style enqueue
wp_register_style($handle, false);
wp_register_style($handle, false);
wp_register_script($handle, false);
wp_register_script($handle, false);
}}}
// Remove styles in front only
add_action('wp_enqueue_scripts', function () {
layout_get(acf_get_fields('group_xxxx'));
});