Foremost: If someone had cancer, that does not mean he would have died immediately. Heck, he could have "survived" it, or at least lived for several more years.
Second: This does not explain the huge numbers of deaths. You can easily compare how many people died of/with lung cancer from 2019 to 2020 and then for 2020 to 2021 and clearly see that COVID made a difference here (called Übersterblichkeit in German, and visible in all COVID-affected countries).
And AFAIK most countries do actually not report a death with COVID, e.g. a car accident, as being caused by COVID.
In other words, this is a common myth from the skeptics department and only serves in undermining COVID-related efforts, even if well intended.