Do not use HTMX for anything other than very simple CRUD apps. The vast majority of the time you'll be wishing you had client side two way data binding and state management. If you want "simple and not React", just use Alpine.js. It has way better ergonomics and features than HTMX and can do essentially everything HTMX can do.
This matches my experience. State management is the key thing - you end up needing to put way more on the backend then you'd otherwise like to. Quick example: something like a multi-step "wizard" is far more difficult to express in HTMX than with any SPA-ish pattern.