Anything doing server-side work is going to have to be at least somewhat custom. The main problem is there isn't a standard "combobox" at all to speak of: we're still mostly stuck with the same carved-in-stone widget set from Mosaic, whereas native toolkits were more inventive even in the late 80s. Where's Athena's 2d panner widget, for example?

I didn't read any satire in the article at all, it just laid out all the built-in behaviors that a proper button has, and how much work it is to reimplement all of them. Something declarative and CSS-like would have been ideal for customizing elements, but instead we got the half-assed Custom Elements API and the completely different DX atrocity that is Web Components.

I can't really fault Custom Elements too much though, it's an imperfect API for an imperfect DOM and it's better than waiting forever for perfection. But I don't extend the same generosity to the Web Components spec.

Correct me if I’m wrong, but my understanding is Google would love to make more web standards native (including selectors which have improved on chrome but are basically broken on safari) but Apple holds back progress in a (borderline?) anticompetitive way

Right, and the article kind of proves your point even a plain button needs formAssociated + ElementInternals to feel native. A combobox with server-side filtering is a whole other galaxy.

If you use a custom select, update your <datalist>, you should be good, shouldn't you?

There are UI components that are not available in native browser controls (infuriatingly: some are only available in some browsers on some platforms), but even then you're better off writing a shim to replicate normal browser behaviour than ruining the experience for everyone because Firefox on Android doesn't have a colour picker.

<input> with <datalist> can provide a combobox

Missing part is dynamically updating the datalist in an efficient way