My preferred technique is to also start with the cover inside out. Then put your hands inside the cyber into its corners. Then grasp two corners of the duvet through the fabric. A bit of shaking to turn the cover the right way out and you are done.
WTF!? I heard before that putting a cover on a duvet was a thing, a problem, a mystery... are ppl making this up? is this a joke I don't get invert, tie corners together and what not... my family and everyone i know do it the way @pablobaz describes it. it's simple and effective. change sheets whenever you feel like doing it, because its easy and fast... endof story
I grew up in a family that had (home made!) blankets and quilts, duvets were not a thing until I moved out on my own.