No, it hasn't. Most farmable land today (90%) lies at less than 100 ft above sea level. If sea levels rise, a large portion of it will be subdued.
Umm,  on that. Even within the USA, that's not even close to true. The so-called "flyover states" are all well above that, and are producing mindboggling amounts of food.
I'd be shocked if more than 1% of farm land globally is actually 100ft or lower above sea level.