That's why I am going to wait till next year to start learning JQuery. Should be stable and mature by then.
The first three examples, which are probably the worst, improve greatly in more modern browsers that include the fetch() API.
In my view even the jQuery examples look a lot better if you can write ES6.
I ran into this issue of jquery silently failing a while ago and will always remember that pain point
If you're developing a user-facing app, then yeah, jQuery is still pretty darn helpful.
The site suggests you try not to make it a dependency if you're writing a JavaScript library. I also suggest vanilla JavaScript for simple pages that need just a smattering of interactivity.