United stunned Manchester City at Wembley in a result which could see Erik ten Hag save his job.
McTominay told the Daily Mail: "Sometimes people can have their opinions and say whatever they want.
"City are an amazing team but we stuck together. I want more moments like that. I came away from that FA Cup final thinking, 'D’you know what, I want more of that'. That is my motivation.
"Every credit to Erik. The scrutiny makes it difficult. That’s the case for any Manchester United manager given the magnitude of the club. It’s only normal but he’s handled it extremely well. I am very, very pleased for him… he deserved that FA Cup.
"It’s not easy when everyone is writing you off and you come up trumps. It makes a big difference to the feeling and confidence around the place. We know as players how big the club is, we expect everything that comes our way, positive or negative."