Figures leaked to the BBC indicate that the Iranian govt has deliberately under-reported the number of deaths from Covid-19. The govt's own internal records show about 42,000 deaths instead of the 14,400 in their official reports.
Iran has a huge number of Afgan refugees and they have been particularly affected. The report doesn't mention why that is but I imagine overcrowded and squalid living conditions may play a part. Although they share a language Afgans are not welcome in Iran.
The Iranians are not the only govt lying about the death rate, they're just the latest one caught doing it.
https://www.bbc.com/news/world-middle-east-53598965