Roon has added support for stereo pairs of Homepods 2nd generation and Homepods mini, but the original Homepods 1st generation are not recognized as stereo pairs.
Please add support for those, it shouldn’t be that hard since it works for the other models.
A workaround I use is to set my iPad up as an endpoint on Roon and then select the audio output on the iPad to the HomePod stereo pair . Clunky I know but it works.