In previous versions I could create HDRI environment maps. I can’t find a way to do it in V5? It seems only to recognize .renv?
I am not sure if I understand the questions completely. An environment (.renv) contains the background plus many other properties. The environment controls the background you can see, not the skylight that lights the scene. This was the same in Flamingo NXT
If you go into the environment and set the Background type to HDR, then you can add an HDR to the background, that will show the HDR in the visible background.
If you are trying to change the lighting in the scene to use a different HDR file, go to the Flamingo tab and change the Sky tab.