That's because there isn't a easy way in htop to discover that.
htop is great, I've used it for a decade, but I didn't know you could hide the threads (Shift+H) until I read this today.
A "View options" / "Advanced" menu item on the bottom bar would help discover these option exists.
I also pressed some key, and some things turned purple, and there's no indication what view is shown, what the purple colour means, and what to do to turn it off.