Based on the available answers, the Nikon Z6 does not appear to offer a selectable 3x3 rule-of-thirds grid in its display options; the built-in grid is the 4x4 style. A practical workaround is to use the center circle and/or virtual level as a visual reference and estimate where the thirds lines would fall relative to that center area. It’s not exact, but many users find it good enough for framing. If you need stricter composition guides, you’d likely need an external workaround such as a marked screen overlay or simply composing with the existing grid and cropping slightly later.