Oddly, to access the commands available when dictating, you have to switch to the Accessibility pane, where the Dictation item offers a button Dictation Commands… which displays the set of built-in commands such as Select previous word. For this, I turned on Enhanced Dictation although I don’t use this regularly, I have used it over several versions of macOS and am familiar with its performance. In Mojave, Dictation is controlled in the tab of that name in the Keyboard pane.

Following a couple of comments here, I’ve turned my attention to dictation and voice control, and how they’ve changed in Catalina.

Making Macs more accessible is a minefield of conflicting requirements in which it’s so easy to address one requirement and lock many other users out.