I used to just cut the top off of the box using a kitchen knife. I would start just below one of the corners, with the box on it’s side, and I sawed through it.
I got some funny looks for that one when I first did it on autopilot around other people lmao.
You know that the serrated lines on the box aren’t great when cutting the cardboard with a kitchen knife is legitimately easier. The blade wasn’t even serrated.