People have typecast htmx as something to use for simple use cases that dont "warrant" getting out the serious guns. There is something to that, but it is limiting. Htmx and related 'back-to-the-server' approaches are a distinct category that could have been explored much earlier but for various reasons isnt
I think you misunderstand HTMX. It’s the revival of an old class of apps in a backend agnostic way. It’s not doing anything new, or anything that warrants a “new class of apps.” It’s a way to build hypermedia (read: content) focused sites. Classic sites like shopping catalogs, forums, admin front ends, blogs, etc.
It’s just jquery/liveview/turbolinks, but backend agnostic and without needing you to maintain much (or any) frontend js logic.
Once you need heavy interactivity (think google docs or figma) it stops providing much benefit.
I mention C# in that ASP.Net MVC + Razor seems like a very clean match to the HTMX paradigm.
Not affiliated with them in any way, but it's made with htmx and some JS for more complex features
As for "new class of web experiences", given that htmx explicitly aims to expand upon what is considered the Old Good approach, not sure if it can provide that