On our ride says change at 60kkm, but if you like the foot to the floor thing, it is recommended earlier. Though I am not a foot to the floor merchant any longer, I do change the fluid at about 30kkm, which is roughly every 2 years, so no big deal.
As for belt stretch, as our belt is of the steel variety, I have not noticed anything odd, and the box is now at 150kkm, still runs great......🤗
Oh, near forgot, CVT has been around for 100 years, watch the video...🤭