When I was a kid, ours opened the doors by jumping at the door handles. Grabbing them and pulling them down.
They even taught their kittens
We had to install all handles so they pointed upwards, just so the cats couldn't grab them
But even that only lasted a couple months until they learned to latch onto them anyway and wiggle around until their weight pulled the handle to the side and opened the door
Handles? Luxury! We have a cat that can grip and twist a doorknob with both paws. She needs a nearby windowsill to sit on, so there's only one door where she can do it.
I don't know if my cat understood what the button did or if it was just because he knew he could get my attention, but my cat knew how to turn off my computer.