What's displayed in the screenshots are typographically relevant variations of the whitespace. 0x00A0 is the non-breaking space, and 0x202F is a narrow whitespace. Both have their own Wikipedia pages where you can look up what to use them for. And while browsers may display them the same as a regular whitespace, because they just suck at typography, the same is not true for word processing or layout software.

Granted, while they can be detected and used as watermarks, although I regularily used them in my text formatting software as well. The resulting text flows better and will not be wrapped in illogical ways. So I don't think they are intended as watermarks, and I also don't think they will be going away again. It's just such a tremendous improvement of the output.

I wouldn't really call these watermarks. If these are watermarks, then someone might call the longer than usual dash a watermark, too:

That long dash is called an em dash — like this one.

My guess is that one of the major motivations of this is to identify their own texts when training future AI models. Training LLMs on LLM-generated data is harmful to their performance and leads to regression, but more and more data they scrape from the internet is LLM-generated. With measures like this they may be able to filter out a significant chunk of the data they generated themselves from future training data.