First PS4 exclusive to pass 20m this gen if I'm not mistaken. Uncharted 4 was at *16,2m last official update (May *March 2019), Horizon at 10m last official update (February 2019), God of War *11m last official update (May *March 2019). Considering Sony never announced 20m for those 3, it's probably safe to assume that Spider-Man beat all 3 of them to 20m.
Actually back in March 2019, Uncharted 4 was at 16,2m. We also got 11m for God of War, then.
There was talk about God of War, doing 20m resently too... spiderman might actually not have been the first.
Sony have just be really quiet about it.
You could probably throw a dice, and use it, to figour if it was Uncharted / God of War / Spiderman, that first hit 20m.
Sony should give updated numbers on game sales tbh.
My source says 10 and 15m, from May, not March:
But either way there is no doubt that they sold very well.
Edit: Nevermind, the article is from May but the sales data is from the March quarterly sales update.