Working on a copy of the duotone image, use Image > Mode > RGB, then save or export as JPEG. Perhaps double check your Colour Settings first so that the conversion to RGB uses an appropriate RGB ICC profile (the more Convert to Profile command is not available for this particular mode). Don't forget to change your Colour Settings back if needed.
I already tried to convert to RGB color mode: It does not convert to RGB, It kind of applied each passes to a specific (see the passes / tones panel. Anyway I tried different color profile, none changed the ouput.