"The X-Plane plugin will be at $HOMEBREW_PREFIX/Caskroom/little-navmap/3.0.17 after installation."
little-navmap is built for Intel macOS and so requires Rosetta 2 to be installed.
You can install Rosetta 2 with:
softwareupdate --install-rosetta --agree-to-license
Note that it is very difficult to remove Rosetta 2 once it is installed.