My dealer said the trailer hitch is currently unavailable due to the ones in stock being recalled.
Fortunately, there are alternatives from both Curt and Draw-Tite, such as here:
https://www.etrailer.com/hitch-2016_Buick_Envision.htm
The hitch can be had slightly cheaper elsewhere, and the wiring harness as well. But etrailer's the only place I found with both, and a guarantee that it will all fit.