Long covid, and CFS, are almost certainly the same disease. The person you're replying to is massively overselling the efficacy of treatment though, most people with this kind of fatigue tend to improve to a lower level of functioning than before their fatigue. Nobody has much idea of what the underlying disease is, and there's no evidence that you can cure it with any treatment

If you talk about ME/CFS, then it is known to be helpful in some specific cases, but not universally. People with ME/CFS tend to be driven by autoimmunity as a primal factor of the disease.

There is a clear problem of diagnosis and intersection of the symptoms. What we call ME/CFS today may be several distinct diseases with overlapping symptoms.

To give you a direct answer: it helps with chronic fatigue, but only if one of the causes of the illness has a metabolic impairment component in it. Otherwise, no improvements are observed.