[edited]
Iinitially I noticed that the in-focus indicators did not appear when using an adapted manual focus lens (FTZ-II, Milvus 50/1.4) so there was no focus confirmation. Peaking does work but in my opinion in many situations it's just not precise enough (focusing on the eye). It could also be an issue related to the use of a third party lens.
I'm wondering if native MF lenses such as the Z Noct do display manual focus assist in the form of the +o- indicators and box changing color when in focus? What about third-party manual focus Z lenses?
However, when I turned subject detection off, it started showing a regular focus box and then the color did change when the subject was in focus, and this also translated to the subject detection once I turned it back on. I'm wondering if there is some kind of a glitch in the implementation. It could also be that I was not able to set the focus so precisely that it would change the color of the box.