I never noticed but you’re right! Glad I never use phone in that orientation. Is so horrible to look at. Absolutely couldn’t live with that on an iPad.The 12 Mini definitely does this too in landscape, it is just much harder to see. At least i would never notice it, without actively looking for it. (Also rarely ever use the Mini in landscape)
The iPad Mini 6 on the other hand is so pronounced that i see it even if i don't want to.