The "therapeutic" dose of HCQ in COVID-19 patients is usually 600mg and up. The therapeutic dose for e.g. rheumatoid arthritis is 400mg or less. These higher doses were linked to arrhythmia and very little evidence of a beneficial effect has been found.
HCQ has been used in petri dishes against many viruses and been successful there. Whenever they use it in vivo, it fails. This is not a new phenomenon. The link below is somewhat dated at this point (May 2020), but I believe it still stands.
https://www.sciencedirect.com/science/article/abs/pii/S01663...
In any case, if the FDA is saying "may not" the drug is not a slam dunk even if it has some beneficial effect. Winning the rhetorical war on HCQ isn't going to make COVID go away or be less serious in a substantial fashion.