You looking at the help for Dorico 1 not Dorico 3, but that doesn’t make any difference here.
You say you are following the instructions exactly but then mention the signposts menu, which isn’t what you want.
The properties panel in the instructions is at the bottom of the screen. Open and close it with the shortcut Ctrl-8, or click the arrow icon in the middle of the status bar at the bottom of the screen.
If something like a time signature is hidden in the score, there is a “signpost” to show you where it is, and the signposts menu just shows and hides signposts, if you want to reduce the amount of clutter displayed on the screen.