I saw a noticeable difference going from a Switch to a Switch OLED, mainly in the contrast in scenes. Greys and blacks can almost look inky in comparison to LCD, and glowing lights (think neon signs) pop out a lot more.
That being said, the topic is the Deck OLED, which I haven’t seen in person, so your mileage will vary.
Just so people understand, there are bugs that simply make you die because 60fps and ladder don’t agree with each other.
I just play it at 30 because of this.