You realise that pneumonia is a description of the symptoms of...

You realise that pneumonia is a description of the symptoms of inflamed lungs right? A symptom that can be caused by numerous diseases including, you guessed it, Covid 19.
it's inflammation on the lungs effectively causing asphyxiation that kills a lot of covid victims. Otherwise it's the stress caused by that asphyxiation that is placed on other critical body systems that may already be weakened that can be fatal.