Can I write a chapter from one character's point of view?

Yes. Open the book and hover over a chapter in the chapter list — a small "POV" button appears (it shows up once you have characters defined in the book's Codex). Click it and pick the character whose eyes the chapter should be written through. The AI then writes that entire chapter strictly from their point of view: their voice, their perceptions, their limits — other characters' inner thoughts only appear through what your chosen character can observe. Pick "No fixed POV" to remove it. Set it before generating or regenerating the chapter; it has no effect on text that is already written until you regenerate.