The person cannot breathe without the ventilation, correct?
You remove the ventilation, in effect suffocating them.
Your action directly leads to death.
But call it what you want, what matters is how you feel about it afterwards.
Right?
By your argument, comatose people who can’t breathe on their own are okay to just switch off because after all they can’t breathe on their own and would die “naturally”.
Yes, it is euthanasia.
Being honest about it would be best.
As I said you are way off base and there is no further basis for conversation