As you state:
An Israel supreme rabbinical court rejected a conversion by a prominent American rabbi who sponsored Ivanka Trump’s conversion to Judaism.
That is, they are supposed to have rejected a particular conversion by the rabbi; not all of his conversions, and not his conversion of Ivanka Trump. In actuality they did not reject the conversion, but they requested details of that conversion (which predated the current central bais din system) and the final result was that that conversion was certified.
In the words of R. Yitzchak Adlerstein:
The recent matter regarding a long-ago conversion conducted by Rav
Haskel Lookstein, for which the Israeli Chief Rabbinate requested more
documentation, generated great media attention because, years later,
he also was associated with the halakhic conversion of Ivanka
Trump....As facts actually have it, Ms. Trump was converted under the
GPS rubric. There is no question regarding her conversion. She was
converted with the full institutional imprimatur. By contrast, Rav
Lookstein’s earlier conversions that pre-dated the GPS...
So again, there was no question regarding her conversion which was conducted following set guidelines. The issue regarded earlier conversions of R. Lookstein, which were done before the GPS (Geirus Policies and Standards Network) was set up. The GPS is an agreement between the Rabbinical Council of America and the Israeli Chief Rabbinate, see here.