In addition, what do historians think in general about diagnosing long deceased historical figures [?]

This is the part of the question I'll address. While I can't speak to Alexander's death specifically, I do have some thoughts on the general practice of diagnosing long-dead persons, and as this is a major part of your question. So I hope that my answer will be acceptable, because really what you're asking is about way more than Alexander, it's about methodology.

When I first read about this theory it seemed a little problematic. The lack of surviving sources from Alexander’s lifetime and from those who were present during his death, coupled with the fact that attempting to diagnose past individuals with a mental illness (as well as psychological evaluations and explanations for why someone did something) is generally frowned upon by historians, got me thinking about wether the same holds true for attempts to diagnose physical illnesses and causes of death where the answer is not clear cut and the circumstances vague.

Right, so I share this reticence, and the medieval field has come down pretty hard on the same side as you. Illustrative of this point are two books which came out around the same time: Rudolph Bell's Holy Anorexia and Caroline Walker Bynum's Holy Feast and Holy Fast. They're both about the strange dietary practices of medieval holy women. Bynum analyzed the whole thing from a cultural/religious perspective and tried to make sense of why women chose to interact with food the way that they did, and what influences were present that helped them to make those decisions. Bell's approach was to try and say that the women were all anorexic. The latter ended up being way less influential a work than the former because as it turns out, historians are less interested in modern medical/psychological explanations for behaviors and more interested in how behaviors were understood and remembered in their own time.

For another example: A lot of my work focuses on Hildegard von Bingen, one of the great medieval mystics. There's been a trend in scholarship to argue about whether she suffered from migraines that could explain her visions. I think it's a pretty useless conversation, because the inner mechanics of Hildegard's brain don't get us anywhere in terms of understanding the historical and religious context of her works, how she understood her experiences and how others understood them. The effort to diagnose seems like more a triviality than a real thesis, because ultimately what's important isn't whether God or migraines or narrative fiction is responsible for Hildegard's visions; what's important is what was then done with them.

But I want to be fair, and say that some medical/forensic historical work has been useful for us. I'm thinking of plague research. It was only recently that scientists working on the Black Death determined conclusively that it was Y. pestis (Bubonic Plague). They did that by studying skeletal dental pulp. So that's not terribly interesting to a cultural historian, but it does tell us certain things beyond what kind of microbe was killing people. Since we know how Y. pestis works and how it's transferred, its presence can tell us all sorts of other things about how goods and people were moving around, what communities were like, and what the actual experience of plague was like.

So this is all to say that retrojecting medical diagnoses onto past people and societies sometimes tells us valuable things and sometimes doesn't. I think that what makes the difference is how well we're able to connect the diagnosis with the wider historical context. Hope this helps.