Foldable phones. They were in the middle of a lot of hype and anticipation, but when Samsung and Huawei released real ones there were too many problems to be justifiable. Software didn’t work properly, because of the messed up screen ratios. The Samsung Fold would break at the hinges, allegedly because “users removed the protection film”. Though it’s a lot better now with the Z Fold 2 and other products, the price is also questionable, and they haven’t gained as much popularity as people anticipated.