I just upgraded to Reason 11 to get the Reason Rack Plug-in functionality.
It is listed in the Plug-In manager (not blacklisted), as is Reason Effects Rack under the FX tab. The Reason Effects Rack DOES show up and I can insert it on an insert or send track, but the Instrument version doesn’t show up anywhere when trying to create an instrument track.
Incidentally I had this exact same problem with a demo of Izotope’s Breaktweaker drum machine I downloaded a week or two ago… it too is listed in the Plug-In manager but doesn’t show up in the choice of instruments to insert on an instrument track.
This is under Cubase 10.5.12 but was also happening under an earlier version of Cubase with Breaktweaker.
Breaktweaker did show up as expected inside my installation of Logic Pro X.