bs"d There is the sentence "Reprove your fellow [but] do not bear sin because of him." Can this sentence be applicable also to parents "Reprove your parent [but] do not bear sin because of him". What if an adult-child is aware of the parent’s mistakes/sins. Can they reprove the parent so as not to bear sin because of him?

The rabbis teach us (Shulchan Aruch Y.D. 240, 11) that in such a case one should ask respectfully, as a question or reminder, “Father/Mother, doesn’t it say in the Torah…?” which is a respectful way of rebuking, and that way the father is reminded without being embarrassed. If after rebuking the parent still doesn’t improve, than at least you have done your share and obligation, and now it’s your father’s issue. With Love of Israel, Rav Ari Shvat