There is no evidence to suggest that inhaling heated or humidified prevents or cures the COVID-19. This claim is baseless.
Steam inhalation is one of the widely used home remedies to soothe and open the nasal passages and get relief from the symptoms of a cold. Steam therapy can help to thin mucus as a supplemental course of action to give some relief when grappling a cold or flu.
World Health Organization (WHO) does not suggest steam therapy with any ingredient as a cure for the COVID-19. It also says that taking a hot shower and exposing oneself to a temperature higher than a 25C degree does not prevent or cure COVID-19. It also tells COVID-19 can be transmitted in areas with a hot and humid climate.
The COVID-19 pandemic has given rise to a lot of potentially dangerous misinformation. For reliable advice on COVID-19 including symptoms, prevention and available treatment, please refer to the World Health Organisation or your national healthcare authority.