At 1:25:33 in the Houdini launch event where all the features are being listed karma XPU says it supports fog box but it does not seem to work and I cannot find information about it anywhere else. Was this a mistake?
Hmm, I just downloaded and tried the production build of 19.5 (19.5.303) and it's working for me. Do you get an error? Is it an old scene? (if so, can you try creating a new Fog Box LOP, in case you unlocked the old definition with an outdated material)