You're right, Manu-smirit had no influence at all and the whole book was composed by Brahmin trolls for fun.
Also, that's from Koenraad Elst, a Belgian academic, pro Hindu and anti Islam, who links the khap panchayats with the Law of Manu :
https://www.academia.edu/4034270/Ma...nism_Nietzsche_and_Hindu_political_philosophy
^so these decisions don't come out of the blue either.
The Manu-smriti is an authoritative compendium of Hindu laws, so it has naturally been applied, to ask for "exact instances" in history (or fictitious epics) is ridiculous, as if every-time someone took notes of it in some report that we could find today. That was my point about khap panchayats/1800s (about mediatization).
There's a reason Wendy Doniger - one of the world specialists on India and Hinduism - calls Manu "the flag bearer for the Hindu oppression of women".