I read that as “there isn’t good quality evidence” not as “flossing doesn’t work”.
If you have plaque on your teeth that doesn’t get removed it turns into tartar/calculus. If it’s between your teeth, over time that can lead to retreating gum and exposed dental necks. It’s of course also something promoting tooth decay.
Removing this plaque with a tooth brush can be difficult to impossible depending on how your teeth are laid out. Floss can be helpful to remove it.
Are you saying this isn’t true?
It is. Did that when this was first announced