I have successfully installed Flamingo NXT5 which is working in my version of Rhino 5 but totally invisible in Rhino 6.
It does not appear in my renderer options or available plugins…
I have tried reinstalling both Rhino 6 and NXT but still get the same.
When I double click the Flamingo 5.5 installer it automatically opens up Rhino 5, even if I drag the file into a Rhino 6 work space.
Try to install the plug manually under this path :
%AppData%\Roaming\McNeel\Rhinoceros\5.0\Plug-ins\Flamingo nXt 5.0 (fd53f8c4-546d-47d1-8820-e66c97645a97)\5.5.18100.1000\5.5
Yes, I had to find the plugin within the installation folder of Rhino 5 and install it from there.
When I open the flamingo file within the 5.5 folder as described it does open Rhino 6 to tries to install but then it generates an error message and says it was built for another another version. I put the flamingo55_release_20180118_0833 that is supposed to work with both Rhino 5 and 6 (that I downloaded from the directed plugin updates location) into this folder and run and it spawns like 30 instants of Rhino 6.