I know people throw the word around a lot - but seriously here...

Your brother sounds like someone in a very deep Depression, he's saying "Men's Rooms are like this in General." as a Mechanism to absolve himself from cleaning his room but also not send himself into a deeper self-esteem breakdown.

By saying the problem is actually not a problem and that's "Just how Men's Rooms are..." is a claim to Nature - a logical Fallacy if you will. In Psychoanalysis this is called: Rationalization.

I'd suggest maybe at a Time when it might not be obvious to him that you're trying to do the following: gauge him about his feelings in a vague way, not existential but just close enough so that he might open up about what is wrong or bothering him either in the long run or short term.

If he does what is called Splitting then you might need to get him to go to a Psychiatrist or Therapist at least.

Why? Well you're brother is showing unconscious behaviour of Deep Depression.

The 1^st one is:

• Withdrawal; by your description of his Room I assume he's in his Room a lot. This is an unconscious Psychological defence Mechanism to experience less stimuli, so that he doesn't get close to the thoughts and experiences/people that he might be feeling is hurting him.

  • ² nd one is as I said above; Rationalization, the claim that his abnormal behaviour is Normal and in part so normal that almost all Men do this, just generalizing.

These are big red flags, and paired with Splitting and Projection this can become very serious if the behaviour continues for months on end and worsen.

Such as he can Start to Act-Out his unconscious suppressed feelings, ( Anger, Confusion and Frustration ) turn passive aggressive and just... well not pleasant.

If this is Already the case OP, which only you could know - then get him to a Psychologist when you can or tell him in a Nuanced way that maybe he should consider it himself.