The reactions that provide the energy for the production of ATP (aka the bulk of all usable energy in every living cell) are oxidation reactions, but the reduction of the oxygen also produces trace amounts of peroxides, which then turn into free radicals that can cause cancer.
So as I tell my students, the number one carcinogen in the world is oxygen...
My dad had a lung condition and ended up with COVID. He was on high flow oxygen for a very long time in the ICU. Eventually it just ripped up his nose to the point where he got a massive nose bleed.
The doctor said it's an inevitablilty because oxygen is so harsh.
The nosebleed forced them to intubate and that was the last time I spoke to my dad.