You upper back is slightly rounding, which is fine. Lower back rounding isn't.
"A Strong Case for The Round Back Deadlift.
This article by Bret Contreras explain it in more detail.
Also, in a Conventional Powerlifting Deadlift, breaking the weight off the floor is initiated with the back, then leg drive kicks in. This method allows more weight to be "Pulled", Contreras notes that in his article.
Dr Tom McLaughlin's (PhD Exercise Biomechanics/former Powerlifter) found the muscle firing sequence in a Conventional Powerlifting Deadlift is Back > Legs > Back; the back breaking the weight off the floor.
This method is very effective for Powerlifters. However, it ineffective for Olympic Lifter.
The Deadlift for Olympic Lifters essentially is the "First Pull". The "First Pull" need to be initiated with legs while maintaining a neutral back position.
The emphasis of Deadlift for increasing strength for the "First Pull" is to properly position the back for the "Second Pull", where the greatest power is produced.
A Conventional Powerlifting Deadlift with some upper back rounding enables more weight to be Deadlifted.
However, upper back rounding dampens power in the "Second Pull" of a Clean or Snatch.
Upper back rounding is good for maximizing your Conventional Powerlifting Deadlift and contra-indicates if for Olympic Lifters.
Your objective determines you Conventional Deadlift Technique.