This is real surprising to hear, as I often see this kinda third inch wide ripple crease in non-marketing photos of em. Is it just not visible when it's on? I could deal with it being visible when it's off.
I had a Z Flip 3 and didn't notice the crease while I was using it. The bigger problem, and the reason I don't have one anymore, is because the damn screen broke (delaminated) 6 months in and Samsung wouldn't fix it.
As I've heard it, it's much less of a problem when you're looking at it straight on and out of bright sunlight. I think it was Honor that released a foldable last year that nearly eliminated it. So they're close to minimizing it as much as they can
I have a flip phone (Razr 2023, which admittedly has a less noticeable crease than most) and it is completely invisible on a lighter background when looking at the display directly. It's only when you tilt the phone to either side and catch the light, or change to a darker background, that the crease becomes visible. They are definitely improving.