I've got a 2018 27" iMac. I have set my Houdini Env file like this:

HOUDINI_UISCALE = 140
HOUDINI_ENABLE_RETINA = 1

It works great I can see! Well, everything but the in app help system.
Does anyone know of an environment variable that I can set to remove the pixelation in the help viewer?

Yeah, that looks bad. You can use an external browser for help with the environment HOUDINI_EXTERNAL_HELP_BROWSER=1

That works great! Thank you so much!