Is there a law that prevents the BOD to provide feedback on violation submitted by a homeowner?
I don’t think so. Depends on where you are, but I’m not aware of any laws (federal or state) that says the BOD can’t provide feedback on violations.
What can be done for BOD members not enforcing the covenants or picking and choosing what they will enforce?
Beyond taking legal action, you might want to remove those board members. That’s selective enforcement what they’re doing.