Kuo says that OLED will bring a few advantages over the mini-LED Apple currently uses in the MacBook Pro 14 and 16, and the iPad Pro 12. It will allow for thinner and lighter devices with more diverse form factors. On a side note, OLED also allows for folding devices.
Kuo doesn't say which MacBook will be the first to adopt OLED, but industry insider Ross Young has said that Apple will announce a 13-inch OLED MacBook Air by 2024.