Personally, I don't think the term "modern JavaScript" makes much sense - it's just a nice-sounding but mostly meaningless buzzword, but I can guess the reason about the disagreement.
Alpine and HTMX are entirely different architectural approach to script webpages, as compared to React/Vue/Svelte/Elm/... approach to build SPA webapps. And the latter approach was very frequently called "modern JavaScript" (and that's why I think it's more of a buzzword now, and less of an actually meaningful term).
"Modern JavaScript" === "Whatever just came out in the past week to six months and has had several articles written about it on the front page of Hacker News"
Somewhat pedantic - Using HTMX represents a modern approach to building a web front-end. However, I'm confident that recursivedoubts (creator of HTMX) would agree HTMX is not itself written in modern Javascript. No Typescript, no modules, no functional programming, no async, etc.
That's poppycock. A library that doesn't require several dozen unrelated libraries to use is a good thing and something we should actually hold up as good engineering.
I'm also confident that recursivedoubts wouldn't like you calling his library not modern. That's just insulting.
Alpine and HTMX are entirely different architectural approach to script webpages, as compared to React/Vue/Svelte/Elm/... approach to build SPA webapps. And the latter approach was very frequently called "modern JavaScript" (and that's why I think it's more of a buzzword now, and less of an actually meaningful term).