I was recently reading some questions here and there saying that "relativistic mass is outdated". I saw someone saying that "outdated" doesn't mean the concept is wrong. My question is what physicists mean by "outdated"? Not everyone was saying that relativistic mass is outdated. Some physicists still say that relativistic mass is not "outdated"

A hotter body is more massive than a colder body (that's an example of relativistic mass, some says it's utter nonsense but they explain it some other way, the more information is available here (a book?) I can't remember anything from the book so not including anything).

When I heard the "outdated" term first then I thought they are actually saying that the concept isn't correct the way others are explaining but the equation is helpful and peoples are misunderstanding it. And their explanation goes this way ..........................................................................