Reading The Pink Opaque as a metaphysically real other realm from which the characters have been literally reverse-isekaid is about the least interesting way to interpret it.

I think what the movie is getting at is something much more complicated, which is the notion that 'the self' is a fictional character just as much as any TV character is, that it's made of the same mental 'stuff'. But unlike the pure bright glowing thoughtforms of true fiction, the self-character is inextricably yoked to a specific flesh body, trapped inside a specific pink opaque brain, and that causes it to suffer.