Probably monitor the On The Road To G’MIC 3.4 thread for the latest plug-in filter postings. Screen shots of settings and sample results are the usual fare. Earlier than that: the “Release of G’MIC X.X.X” going back to Release of G’MIC 1.7.6 around September 2016. All those threads, including the current “On The Road To…” have the “changelog” tag. Filter G’MIC posts on that will pull them all up.
As for the “Grand Catalogue of Every Gmic-qt Plug-in There Is!” — as a practical matter, it’s the plug-in itself, really. The web site catalog is probably waiting for someone with time on their hands. Lots of time on their hands…