The thyroid is I think far enough away from the main cervical lymph nodes and also the olfactory lymphatic drainage pathways too that I don’t think you need to worry about thyroid removal affecting the lymphatic drainage there.

That being said your lymphatic drainage could still be affected by many other things. Eg do you have chronically inflamed sinuses? Difficulty breathing? These would be things pointing towards greater obstruction of the drainage pathways as it points to inflammation potentially impacting the flow of lymph out of the head/brain.