I dont understand why he can not take en passant on move 28

In order for Black to take en passant, their pawn would have to be on f4, next to the g4 pawn. The way en passant works is that if Black's pawn would have been able to take White's pawn had it only moved one square, it can still take even though White moved two squares. Since in this case Black would not have been able to take if White had moved one square (to g3), Black cannot take en passant.

Thank you :)