Is a person, who is mentally ill and does not pray, responsible for not the disbelief of not praying their whole lives since they are not mentally sane?

My father takes medications for many things but the side effects for taking them long term is a person loses their sane mind. They may have personality changes or have bad decision making. Due to this he does things which aren't normal for a mentally sane person and he does not pray. Will Allah hold him accountable?

Obligation/Taklif is lifted from mentally ill or insane people. So if the mental illness affects him and he is not in his right mind (and that’s why he doesn’t pray) then he is not liable for that and Allah forgives him.