Mount, 25, joined United in July 2023 in a deal worth an initial £55 million ($70 million) but has played just 28 times for the club, scoring a solitary goal.
On Thursday the England international made his first start since August, playing nearly an hour in United's 3-2 win against Bodo/Glimt in the Europa League.
"First thing is he is working really hard," Amorim said of Mount. "And then you have to understand the human also.
"He wants this really badly and that is the most important thing. I think he has proven to all of you that he is a talented player. He was a European champion (with Chelsea), so we believe a lot in him.
"He has to stay fit. Like all the guys in the team, they are quality players, they have to improve, believe in themselves and he did a great job (against Bodo).
"You see some moments and details that you can see that Mason Mount is a proper footballer, so we believe a lot in him. I especially believe a lot in Mason Mount."
Amorim, who drew his first United game at Ipswich last week 1-1, said due to the relentless schedule of matches, he has been walking his players through tactics.
The Portuguese, who replaced the sacked Erik ten Hag earlier this month, arrived at Old Trafford during the international break and has had little time to get his ideas across.
"I was a football player," said the former Portugal international. "Football players, videos more than 12 minutes? Forget it! Because they lose the concentration.
"So, we have to work on... imagine there's an indoor stadium. We have that (at the Carrington training ground). Instead of video, we do it like walking and jogging. It's a way to do it. Showing some videos."
United, who play struggling Everton on Sunday, are 12th in the Premier League after a poor start to the season, which cost Ten Hag his job.
"It's going to be a different match with a lot of fighting, long balls, second balls," he said. "They have a quality coach that understands the league, that understands the moment of the opponent.
"We need to have the ball because we have a short time to recover. We need to rotate the team, so I hope for a win and I hope to see different things in my team.
"Improve like we did from Ipswich to now, with Everton without training. But I expect to see different things and better things."
