Sorry about that. Now I finallyI see it in the active key settings under Settings > Advanced Features > Active Key. I thought it was a toggle, but it's just described there and is apparently always supposed to work.Confirming the ActiveKey as a HW camera button option on Nougat as well. I use it almost all the time when taking photos.
Unfortunately, I can confirm that it doesn't seem to work on the 3CRG2 build.