Come on. What could be so secret? But yup, Sharon Zardetto, writing for TidBITS, reveals some stuff that, at the very least, is not well known. For example:

If an item has a dedicated function key—as do volume control and screen brightness, for instance—press Option and the function key to go to its preference pane. This trick also works with the Touch Bar.

Lots of detail here, terrific work.