So, my friend suffers from gender dysphoria along with major depressive disorder, but along with these things he thinks there are more mental issues affecting him.

For example, when I look into a mirror, I still see my face. But what happens when my friend looks into a mirror?

When he looks into the mirror, he doesn't see himself, he doesn't see a person at all. It's like a thing, like a robot pretending to be a person, and he's stuck inside of it. Sometimes his skin itself even feels like a cage, and he can't get himself to leave.

Does anyone know what this mental illness could be, and what it's called? Or if there's anything similar?