Power of attorney is granted to allow you to do stuff they want for them as if you were them. It does not allow you to override their clearly-expressed will.
To override their will you would need a guardianship which (at least in the US) you are not going to get until they are quite far gone with dementia.
TL;DR at least in the USA your parents have a legally-protected right to be as stupid as they want and you can’t use the legal system to stop them
Power of attorney really does not help at all.
Power of attorney is granted to allow you to do stuff they want for them as if you were them. It does not allow you to override their clearly-expressed will.
To override their will you would need a guardianship which (at least in the US) you are not going to get until they are quite far gone with dementia.
TL;DR at least in the USA your parents have a legally-protected right to be as stupid as they want and you can’t use the legal system to stop them