I'm unfortunately not there physically to help, but my mom has this light switch she needs to remove temporarily and replace the plate. Her "handyman" installed it 'brand new' within the past few years. I told her it looked like it was from the 80s haha. Anyways, she apparently cannot remove the knob for the life of her, shouldn't the knob be able to simply pull off without breaking?
I had to replace one that looked almost exactly like this once and basically I had to just break it in the end.