Let's win this game by playing the only winning move for White.
If Black's King is on any of the red squares when it's White to move, this position is a draw.
With Black's King on b6 or b7, Black will simply capture the pawn on the next move.
With Black's King on c6 or c7, Black will play Kb7 on the next move and be able to either capture the pawn or occupy the promotion square by playing Ka8.
With Black's King on a1, a2, or a6, it's impossible for White to move their Rook away from the promotion square with tempo as no checks are available. White either has to move their Rook and lose the pawn, or move their King. The White King has nowhere to hide, so black can just check White forever.
If the black King is on any square other than the red squares, it is a win for White.
With Black's King on d7, e7 or f7, White can play Rh8. Black can't respond with Rxa7 due to Rh7+, winning the rook on a7. The best Black can do is to delay the eventual loss.
With Black's King on any other square not mentioned, White can move their Rook away from the promotion square with a check and promote their pawn on the next move.
With Black's King on b6 or b7, Black will simply capture the pawn on the next move.
With Black's King on c6 or c7, Black will play Kb7 on the next move and be able to either capture the pawn or occupy the promotion square by playing Ka8.
With Black's King on a1, a2, or a6, it's impossible for White to move their Rook away from the promotion square with tempo as no checks are available. White either has to move their Rook and lose the pawn, or move their King. The White King has nowhere to hide, so black can just check White forever.
If the black King is on any square other than the red squares, it is a win for White.
With Black's King on d7, e7 or f7, White can play Rh8. Black can't respond with Rxa7 due to Rh7+, winning the rook on a7. The best Black can do is to delay the eventual loss.
With Black's King on any other square not mentioned, White can move their Rook away from the promotion square with a check and promote their pawn on the next move.