For what it's worth, I mentioned HTMX to a Ruby developer friend, and his reaction was "oh, like Turbolinks", so I think the mindshare was probably there first. That having been said, HTMX is my preferred way of making dynamic frontends now. I've never been a React developer, but I've always found SPAs way, way overused.

Yeah, Turbolinks was huge throughout the Rails era—I remember it even being part of the random beginner tutorials that I did back in the day. I only ever heard of intercooler.js after htmx was announced.