Do you move your (lower) back back and forth during the exercise?

I find mixed recommendations online. so far, I think it is better to keep the lower back stiff and focus on arms, shoulders and upper back. Also, you don't move the back when doing barbell rows which is the same movement.

For example, jeff nippard moves his back at 6:00 min in this video https://www.youtube.com/watch?v=PAXkl-AdJFg not as strong as others do, but still.

Here, they keep the back perfectly straight https://www.muscleandstrength.com/exercises/seated-row.html

In my gym many people (all that I witness) move their back.