I don't understand the relevance of any of this, but I think I've done a fair job outlining my points above. Let me give my best summary: the execution environment used by a library's (example) documentation is independent from learning the API of the library itself. I agree that newcomers to JavaScript may find plenty of confusion there, and I'm sure a decent chunk of D3's users may be new to web-programming in general, but it's not the job of D3 maintainers to account for that.
I actually think our back-and-forth is a perfect example of why open-source is so painful to work on.
D3 is one of the best documented libraries out there is. There are multiple books, hundreds of hours of youtube videos, and most importantly, dedicated maintainers (Mike Bostock, Philippe Riviere, etc.) who've poured hours into additional sources of documentation and are very responsive on GitHub issues.
The unfortunate outcome here is that users have come to expect this sort of high-quality support and documentation (again with the italics, who does this guy think he is???). Every D3 submodule has standard api documentation, sure, but thats expected of all libraries these days. However, the additional example documentation (again, nobody got paid to make this material) for the most recent releases has been migrated from bl.ocks.org (a now defunct open-source service users didn't pay for it) to Observable Notebooks. Now, Observable is a VC-backed business, yes, but the documentation is still completely free. In this thread, you mention you don't like this, so in at least one online conversation where D3 comes up, you actively advocate against using it out of principle! (Couldn't resist!).
Of course this is just my viewpoint on what has transpired, and I'm likely articulating it in a more-inflammatory-than-reality manner. But I'd prefer to have D3 documentation in the form of free, interactive Observable Notebooks rather than to have no documentation at all. Even more so if it helps out the authors of the open-source library.
As a tip for those who have difficulties going from the reactive Observable model to vanilla js -> you can always just take an observable notebook and ask AI to convert it to a set of vanilla files for you.
PS - Sorry for the novel, at an airport!