I’ve got two different PEX tubing install guides and neither specifically mentions fastening the rough-out/stub-outs for hot and cold water under sinks securely to the wall framing.
I have Wisbro specs and the 128 page guide published by NAHB/PATH/PPFA.
Anyone have any other sources that sez stub-outs need to be fastened?
It depends on what type of stub out is being used. Most that stub the PEX out of the wall use a 90 degree drop ear that is connected to the stud. Some use copper stub outs also with connectors. It is pretty tough to bend the PEX so it sticks straight out without a connector of some sort.