Execution: Local with PHP

You could execute a workflow manually in your own vtigerCRM extension or PHP file.
You only need the following PHP Code:

   require_once("<rootvtigerCRM_Url>/modules/Workflow2/run.php");
   $current_user = new Users();
   $current_user->id = <executingUserID>;
   $current_user = $current_user->retrieve_entity_info(<executingUserID>, "Users");
 
   $objWorkflow = new WfMain(<workflowID>, false, $current_user);
 
   # If you have a recordID use:
   $newObj = Workflow_VTEntity::getForId("<recordID>");
   # If you don't have a associated recordID and the workflow don't access fields you could use:
   # $newObj = Workflow_VTEntity::getDummy();

   $newObj->loadEnvironment(array("variable" => "value"));        // [optional] Variables, which will be available inside the Workflow in $env
 
   $objWorkflow->setContext($newObj);
   $objWorkflow->start();