For 18.04, Gnome (for other desktops, see below):
The same as for 17.10 - as seen in the other answer.
When Tweaks tool is used, especially with various extensions, in order to have the above option be sure App Menu is not disabled, including in per-extension settings.
For example, with the Dash to Panel extension, which creates an all-in-one dock/panel (the dock is merged into the panel) and brings the favorite and running applications icons onto the panel, you have a specific settings button under which you can enable/disable App Menu:
But, with the same extension, as App Menu is not really needed anymore, it can be disabled without losing access to the Nautilus settings, as the Nautilus/Files icon that now appears onto the panel (when the program is opened) has the "Preferences" option in the right-click context menu:
The Nautilus settings are also available as
gsettings, editable through dconf Editor - as already indicated by this answer - at the level
Outside Gmome, namely in Ubuntu Budgie, the left-corner button that gives access to those options (but which is missing in Ubuntu 18.04 Gnome) is not missing with the same version of Nautilus 3.26.3.