FileMaker Script Debugger, Data Viewer, Layout Objects window, etc

If they are not windows as defined by the macOS, then KM will not be able to "see" them, or reference them.

The best window discovery tool I know of is further down in the topic you referenced:

So, if the objects you want to access do not appear in that list, then you will have to resort to AppleScript UI scripting, which can access any element on a window. To discover these objects on a window, try this tool, also by @ccstone:

Macro: Front Window Analysis Tool for System Events