Ah, some progress!
From https://www.reddit.com/r/OpenRGB/comments/l2ramj/do_i_need_the_kernel_patch/ after modprobe i2c_dev openRGB recognizes the ASUS Aura SMBus device.
Now I can set a color cycling pattern like Rainbow, Spectrum, etc., but all single-color modes like static, breathing, etc. are green, regardless of what color is applied.
There are also only six primary colors to choose from, very different from the dozens of colors that are shown in screen captures on the internet.
Perhaps this is due to the missing kernel patch. Or not.