In his thread, Ryan says he used the denoiser at 4x the resolution and downscaled the images:
You’re welcome for the 50% off 
By the way, for those experiencing issues on the Blender Market with the coupon codes, it’s a bug on their website. To workaround it, you can log out, clear your cache and cookies, log-in, and (important ! only after log-in) add the E-Cycles version you want to the cart. Then you will get E-Cycles 2021 at the upgrade price