Considering that I got rejected after my onsite interview, would it be stepping my boundary if I send a message in LinkedIn to my interviewer to ask for feedback?
Its so fucking annoying that recruiters dont give real feedbacks verbally... like who gives a shit, do people really sue over something verbal?
They could
People will sue for literally anything and everything. For example - one candidate not so long ago was really under the bar, poor communication, etc so we ended the day early to save interviewers time. They threatened to sue for discrimination, no grounds whatsoever.
You can, but I would expect them not to answer, or to answer in broad terms, since the answer they give may become a legal liability