The “black fungus” disease is also called mucormycosis, and you might find more medical/scientific information using that term. It’s not really new, just rare because you usually need either a weakened immune system, uncontrolled diabetes, or both to come down with it.
Prior to covid-19 it would crop up in, as I said, people with uncontrolled diabetes, people with advanced HIV/AIDS, certain types of cancers, people with kidney failure, organ transplants, people with long-term corticorsteroid or immune suppression therapies and a few other somewhat rare/unusual conditions
Getting a bad case of covid-19 can certainly impact your immune system. The use of steroids likes dextamethasone can be life-saving, but they also suppress the immune system. See where this is going? If the patient is also diabetic you have a person that the fungus views as a tasty meal.
From my very limited information, it seems a lot if not most of the affected patients in India had that trifecta I just outlined above: covid-19, steroid therapy, and diabetes. (Which is yet again another very good reason for diabetics to do everything they can to keep their blood sugar under control - you want to minimize risk factors here.)
So, in the case of your husband…
Does he have covid-19? No? Then it is unlikely he’ll catch this.
Does he have diabetes? No? Then it is unlikely he’ll catch this. If yes, then keep that blood sugar under control! (As much as possible - I do realize nothing is perfect)
Is he on any sort of steroid therapy? No? Then it is unlikely he’ll catch this. If yes - get a covid vaccine as soon as possible, avoid crowds, wash hands, mask up (with an N95 or equivalent, the sort that protects you as opposed to mostly other people), and do everything possible to keep the current health situation under control.
Does he have the bad fortune to have the trifecta? Diabetes, covid infection, and steroid therapy? The good news is that even when a person has multiple risk factors they still probably won’t catch this. It really is a rare disease. But wait - if that’s so, why so many cases? Because India has a billion+ people and a massive outbreak of an epidemic disease so even though the risk for each person is very low there are enough people that we’re seeing an uptick in cases. Which is yet another reason to try to avoid or, failing that, control a pandemic (which, by and large, the world has NOT been doing a great job of).
If he’s got the trifecta then he should get reliable information on signs and symptoms so if this does crop up he can get immediate treatment. Even so, the rate of this infection in India is, based on a quick google, less than 1 in a million. It is very rare even in circumstances that are pretty dire medically speaking. I’m not sure, but it looks to be somewhat on par with needing a lung transplant after covid - very rare overall, although if it hits you it’s pretty horribly serious.
Here is the wikipedia section on signs and symptoms. They also have a few icky pictures.
Oh, and here is the CDC website on the disease which is, as I suspected, under “mucormycosis” rather than “black fungus”.