JC_ProPlus that's what I'm using in the Wordpress extension:
use Carbon\Carbon;
use Flarum\Extension\ExtensionManager;
use Flarum\Suspend\Event\Suspended;
// [...]
/**
* @var $manager ExtensionManager
*/
$manager = app(ExtensionManager::class);
if ($manager->isEnabled('flarum-suspend')) {
$user->suspended_until = Carbon::parse('2038-01-01'); // Value used for "indefinitely" by the Suspend extension
app('events')->dispatch(new Suspended($user, $actor));
}