But afaik a big portion of them didn't actually die because of the virus directly, but they instead were infected with it in the past and in the fight between the immune system and the virus the immune got so weak, that other viruses could attack the body with its defences down. So the person technically died to other viruses and only indirectly to the coronavirus.
How did you know this? We have no data to suggest that any of the statements you made here are correct.
The cause of death is determined by the treating clinician or at post mortem. Covid-19 attacks a number of organ systems including the lungs, heart, liver, kidneys, pancreas and gut.
It's pretty obvious to the treating clinician what the cause of death is. The immediate cause may be the heart stops, but the underlying cause may be inflammation of the heart caused by virus, or because lack of oxygen triggers a heart attack and so forth. In short it's a clinical decision. If someone dies at home, then a post mortem could be done but in this current pandemic, it would be unwise and dangerous to do so without full protective equipment.
“We’ve made it very clear, every time I’ve been up here, about the comorbidities,” Birx said Wednesday during the White House press briefing. “This has been known from the beginning. So those individuals will have an underlying condition but that underlying condition did not cause their acute death when it’s related to a Covid infection.”