I don’t really see if there’s now an option to further improve the select with JavaScript to add, for example, a search textbox for filtering.
And what about the nearly unusable (on desktop) <select multiple>?
I don’t understand the hatred for select multiple on desktop. It’s a list box that uses standard UI conventions that have been present for three or four decades now.
How about the literally unusable <select multiple> on mobile? You can't select more than one option on a touch screen...
search textbox: would be supported under the even more customizable combobox element
select multiple: both the enhanced select and combobox plan to support this
Combobox: https://open-ui.org/components/combobox.explainer/
Enhanced Select: https://open-ui.org/components/customizableselect/