I am so sorry for what happened to your husband. I have been through similar situation but much less serious. Two years after Covid I developed pneumonia and then low oxygen levels. After being hospitalized twice I came home with oxygen. My oxygen has dipped to low 70’s -80’s. I have not used it for months now but oxygen level is often around 90 - 92. I am fatigued consistently and have post Covid symptoms. I was never told the low oxygen levels were from Covid but have always wondered? I will pray for your husband and wish you both good luck.