Wooooaahhh it’s working now! It was weird, I didn’t change anything in the settings for the Cycles Add-on menu. I guess it just wanted me to look at it, then it worked? Computers… so fickle.
The viewport denoising works really well. I loaded up a big scene I’ve been working on and it’s surprisingly responsive. In fact, loading cycles in the viewport felt instant, much different from 2.83. Interesting! Although both the viewport render and the image viewer render cause crashes if I throw too much geometry or textures at it, even if 2.83 can handle the scene fine. Bound to happen with this sort of setup I suppose. But nonetheless, this is amazing! Thanks again for sharing. It’ll be interesting to see how long this patch works on future versions of Blender.