أحسن الله إليك If a person claims that a haram thing is halal and vice versa for anything in the religion(in small or big issues) is that person going to stay in the hellfire forever?

Making takfeer of an individual by name is a very very dangerous matter that I warn my brothers and sisters from as this is the job of muftis, courts, judges, and those in authority. However, when we study them, we only study the general ruling academically which is not applying rulings to individuals.