I think it's inevitable that the "number of players" figures will rise with gamepass subscriptions so not too surprising.
Probably 25m+ have access to this game for free.
Gamepass only had 10m subscribers at the start of 2020 so when Forza Horizon 4 came out in 2018 it would no doubt be less than 5m.
So yeah it absolutely should destroy FH4 player numbers.
Gamerscore:20,000 - Trophies:3,800 - Nintendo Awards: -1
My Xbox Series S is my baby. It grew up into an X.