Cutting that thicker plastic can really be painful (and injurious). Scissors will tend to push one side up and the other down. The newly cut plastic is razor sharp. The plastic requires a lot more force than regular paper scissors are meant for.

I have an indoor pair of tin snips for just this occasion. Cuts smoothly through the plastic, and keeps my hand further away from the sharp bits.

My Leatherman Wingman multi tool has a “package opener” which is perfect for opening plastic clamshell packaging.

I also use tin snips on these packages!

that is why you have to locate the spot on the package where the cut has already been started and use the grove that is scored into the package.

Cutting paper with scissors is easy. Cutting wooden boards with scissors is hard. Modern packaging plastic is more similar to boards than to paper.

'most people' -> especially the elderly have serious problems with this (as well as with various food packaging). Scissors range from industrial shears to household scissors and especially the latter are not going to be able to cut this stuff without risk to the user, it's actually bad advice (the scissors can flip sideways suddenly due to the asymmetric loading and the relatively high force required).