The other day, I reported that Google Drops Supplemental Results Query Command. I suspected that Google will drop the supplemental results command and possibly the supplemental results label forever. I still feel this will happen but a new way to find supplemental results have been discovered.
A search for site:https://www.seroundtable.com/& will return supplemental results for this site.
So the syntax is currently www.domain.com/&
Forum discussion continued at WebmasterWorld.