Turbo is more or less a continuation of Turbolinks, which has been around for ages. The Turbo repo goes back to 2015 (htmx starts in 2020), but Turbolinks is many years older. Of course there have been other "htmx-like" frameworks before; who even knows who or what was first at this point?

I don't think "feels like 37 Signals took the same idea and is trying really hard to sell it" is very fair (I've never seen them try to "sell it" at all, much less "very hard"). Regardless, you're allowed to "steal" ideas.