In the secular society, a “prenup’ generally is a document to preserve one side’s finances in case of a divorce (to discourage people marrying for money and trying to “cash’ in in case of a divorce).
As far as I know- the so-called “prenup’ that is being discussed here is a document that binds chosson and kallah to bring their differences in front of a bais din when the marriage has irrevocably broken down. It was introduced some years ago to prevent the case of agunos- when the husband is holding up the get -generally to extort money.
It was drafted by many Poskim and ,at the outset, there was opposition by some Poskim as it may be a ‘get me-usah” (a get that the husbsnd was forced to give). However, after reviewing the document that was in question, most Poskim concluded that it is NOT a “get me-usah” and , as mentioned by many, is being used in a number of marriages.
In view of the problem of agunot- a serious problem, by the way- one should not criticize Rabbonim that insist on having this document.