I have a lower rating than you and you probably know it better, but when I play this as white I try not to allow b5 (by playing a4 and stuff), to block the Q side before starting the attack on K side.
And the doubled f pawn did not look nice...
Anyway, I am also courious about a better player opinion...
In my opinion, you underestimated the power of black's queenside pawn majority:
Allowing 8. ... b5 was the first step.
Then 18.Rac1, taking away the pressure on his a-pawn.
Then 22.Rfc1. Better was Rxc8 Rxc8 Rfa1.
From then on, you were positionally clearly worse.
Other remarks: I prefer 25.Qxf4 (instead of Nf5), and 27.Kf1 (instead of Bf1). But these are tactical considerations, not as important as the strategice one above.
2 edits
Originally posted by Mathurine8 Bf4?
Can anyone tell me what my fundamental error was in this game?
Game 2803100
8. a4 would be better in this (now) Benoni style position, then you can plan to attack that d pawn with Ne2 - c4 and Bf4 although black, of course, should not allow this.