Generational talent is self-explanatory: talents that are so rare they show up once or twice a generation. Regardless of what you think of Neymar, just how many wingers from his generation of his overall ability can you name? At his best he was a top goal scorer (40/30 goals), a top playmaker (near Messi's level), and a top dribbler (also near Messi's level). Now tell me, who comes close? Salah has the goals, but not even half the dribbling, sense of touch, game sense and creativity Neymar had. Hazard also comes to mind, he rivaled Neymar in dribbling and creativity but never in end product.
That's what makes Neymar a generational talent, because you can't find anyone else like him from his generation.
If you can name any other U23 player scoring 40 goals or so a year like Haaland and Mbappe are, be my guest. If you can't, these two are generational talents. No one else comes close. Regardless of the results their teams pull in whatever match you can think of.