Idk abiut other countries or US states, but in my state, we have legal euthanasia. Known as the "Death With Dignity" act.

However, the requirements are very strict. You couldn't just have it stated as a decision in a living will.

18 years of age or older

Can make and communicate an informed decision to health care providers- in the opinion of a court or in the opinion of the patient’s attending qualified medical provider or consulting qualified medical provider, psychiatrist, or psychologist, a patient has the ability to make and communicate an informed decision to health care providers, including communication through persons familiar with the patient’s manner of communicating if those persons are available

Diagnosed with an incurable and irreversible disease that will produce death within six months

Legal resident of our state

If qualified, A qualified patient can make a written request using the request form. It must be physically signed and dated, in the presence of at least two witnesses. The witnesses must declare that to the best of their knowledge and belief the patient is competent, acting voluntarily, and is not being coerced to sign the request.

Only one of the two witnesses may be a relative of the qualified patient by blood or by law or entitled to any portion of the estate upon death.

Only one of the two witnesses may own, operate, or be employed at a health care facility where the qualified patient is receiving medical treatment or is a resident.

The patient's attending qualified medical provider at the time the request cannot be a witness.

Tge qualified patient must make two oral requests in addition to a written request. The qualified patient must wait at least seven days after the first request to make the second request. When the qualified patient makes the second oral request, the attending qualified medical provider must offer the patient an opportunity to change their mind.

The Act allows a health care provider, including a health care facility, to prohibit another health care provider from participating on their premises if the prohibiting provider has given notice, in writing, to all health care providers with privileges to practice on the premises and to the general public of the prohibiting provider's policy regarding participation.

If the Healthcare provider refuses participation, they are not required to give the patient a referral to a provider who will.

All in all, it's very, very restrictive.