It seems that when you try to create a new record for a Task from workflow. You cannot set the Relation to another object. This selection does not exist on the task .
So the Task is created properly but it is not connected to the required record. And even if you try in second step to edit the created record there is not option to set the relation. I do not think that it is a good idea to run external workflow thought other software like n8n to send the task id and the object type and the object id to create the task relation.