Hi, I replicated the problem by renaming the file AudioPlugs.srf inside the C:\Program Files\Steinberg\Cubase 12\VST3\Cubase Plug-in Set.vst3\Contents\Resources folder , i.e. making it “invisible” to Cubase.
Now, if this file exists there, it may be corrupted, and if it doesn’t, this is the expected behaviour (no plugin editor switch menuItem).
In either case, you probably have to get a fresh copy of this file from a friend. I would post it here, but it’s around 100mb. Note that simply re-installing Cubase won’t help, since I’ve tried that and it’s not regenerating the missing file.
And here’s a link of a similar thread which led me to these observations: Stock VST Plugins suddenly showing only generic GUI. Cant switch back - #4 by Withamation