I've loaded an example file from the help pages which uses the RBD Cone Twist Constraint Properties sops node.
When I select the RBD Cone Twist Constraint Properties node and hit return in order to make edits I am told to select one or more constraints.
No matter where or how I click in the viewport I am unable to select or deselect any constraints whatsoever and I've been unable to find any information on how to actually select one of the existing constraints.
I can use the command Ctrl+A to select all constraints, but then there is no way to deselect them again.
Maybe there's a bug in here somewhere, but I would've imagined that you could just click on a constraint to select it and click off it to deselect it.