@jlampel Here's a screenshot from Blender 2.91 on a MacBook Pro. I know Cycles does path tracing and it takes quite a while before viewport's rendered region becomes clear from a very checkered, blocky output.
However, I waited around 6 seconds before this screen grab and you can see that still the noise hasn't drowned out; giving it a minute more doesn't help either. It stays the same. It's really hard to understand the output of my work in the Shader Editor due to this. Are there any settings I could tweak to get this working?
Your Viewport is set to render with 32 Samples, you can wait for days, but the image won't get any clearer. You need more Samples to get rid of the noise, so increase that number.
You can also use the (Viewport) Denoising (below Adaptive Sampling).
Thanks for the suggestion spikeyxxx ! Increasing this setting does ameliorate the problem; understandable. I don't want to increase this too much either as it'd slow down the viewport display and general smoothness of Blender.
Before posting this question, however, I did notice in this video, Lampel too has the same 32 samples set for viewport and his viewport looks a lot better (less/no? noise). Why is that?
He probably uses Viewport Denoising. I can get a clean image with 3 Samples with Denoising, but with my old hardware that takes quite long and my viewport becomes very unresponsive. (When you have Optix then thsi Denoising works really fast.)
I don't have viewport denoising on (but that would help!), but it could look cleaner due to a couple things. In the video I'm only dealing with super simple shaders that don't create much noise whereas your example is a bit more complex, and I'm recording at a high resolution, downscaling it, and it's getting compressed on output which will make the colors converge a bit and look smoother by the time it hits your eyeballs.