This does seem a bit like fear mongering as it plays on the lack of public understanding over illness.
Any lower respiratory tract infection, especially one that lands you in intensive care, can cause scarring and damage to the lungs.
Any illness can provoke delirium, especially in older individuals with many pre-existing risk factors for delirium. Delirium is bad, whether it merely a sign of poor underlying health status or an actual cause, mortality one-year post delirium is around 50%.
Any individual admitted to hospital will have some deconditioning. For older individuals, not moving, they may lose up to 1% of muscle mass per day. When reserves are low, it’s hard to bounce back after that and many will not return to pre-morbid functioning.
Covid-19 is not a great disease to get but it’s not Ebola. Individuals at any age can get quite sick from it, although healthy younger individuals will probably do okay. Like any acute illness, it is not great for the frail elderly due to both the actual illness and the sequelae (see above).