This was an interesting loophole in the rules that was exploited often by the faster receivers in 2023.
Essentially, they would go into motion and then would take at least one running step towards the line at a forward angle, with continued motion parallel to the line otherwise still to be allowed unless it is abruptly before the snap of the ball.
If you watch the video clip linked in the article, you can see examples of the now outlawed motion before the snap via the change in the wording of the rule on motion before the snap by backfield players in the NFL.