HTMX is a great choice for an app that only needs forms, validation and partial template rendering, though CSS view transitions are making partials less relevant for server side web applications.
For things with heavy interaction (drag and drop, chat etc.), I find the code to make it work with HTMX is just too clumsy to work with as a mental model.
That's exactly what the article is saying.
multicardz is heavy drag-drop ui. totally based on htmx (I still need to get data from a backend, I use htmx to do it for a number of reasons.)