Showing up white means nothing.
The value could be above 1 to match the height level and just not be normalized.
I have no idea why you would expect it to be normalized actually. Its far easier if it is not, so that it can be applied and used where needed.
To visualize it normalized, probably divide by the landscape’s overall height (negative and positive, above and below world 0).
That should give you some sort of a debug view.
Perobably also clamp between 0 and 1 before rendering, since values above 1 are pointless to “seeing” anything.
If it really is not working, then there’s a few options to check.
Make sure custom depth is enabled and used. Obviously without it enabled and set up, both landscape and project wide you will not get outputs.
Make sure it works elsewhere (like a PP) so you know the engine isn’t bugged.
And make sure that the RTV is properly set up to capture it.
Alternatively - and only if you positively cannot get an output from the RTV due to an engine bug.
Take WPO’s Z, divide it by the landscape’s overall height and you have yourself the expensive version of an height output.
This only includes the landscape, and is rather expensive.
You are asking the landscape to compute the value for each pixel (of landscape) on screen.
It will not include other meshes or objects like the RTV can and should, so its only useful for some things;
An example would be using a texture stretched vertically to define color ranges for the landscape to blend into, essentially simulating terrain stratum.