Okay so my immediate thoughts after watching Wild Blue Yonder was that the No-things are a like an analogy/reference to AI images.
Now I'm neither an expert on AI nor on Dr. Who. The two special episodes I've watched so far are in fact the first Dr. Who episodes I've opted for.
But just the way AI images look correct at first glance but when you look more closely for the details - number of fingers/legs, hair etc., they're off. The same is the case with the No-things at first. They're unable to get a hang of their bodies.
However, I've seen people mentioning now that even AI has upped the game and is becoming more and more accurate. The No-things too become more and more perfect near the end of the episode.
Just my two cents here. Apologies if anyone has already said this before me.