This is evidence; it isn't great but it also isn't conclusive. We'll need to wait longer for something a little more decisive. A twitter link is also unhelpful because we only get a blurry abstract to go off.

The happy dream is maybe hydroxychloroquine has prophylactic tendencies since it is something people can take long term to be at a substantially lower risk vs catching COVID. The abstract doesn't really show much either way on that front.

Spitballing as an amateur, I suspect once someone has actual symptoms or is verging on a serious case it is too late to help - what is a drug supposed to do, regrow a busted lung? It comes to a point where the virus isn't what is killing you, it is the damage the virus did while breeding and/or the immune system overreacting fighting back and going haywire. Antivirals should help but aren't expected to be magic for either of those things.