He doesn't play like FDJ. Never played like him in the youth teams either. FDJ is like a 10, playing as a 6 (like Iqbal). He can dribble and progress the ball through that. They have through balls in them compared to the average midfielder.
Garner was a talented youth player who was always the more defensive presence compared to his midfield partners. Unlike McTominay, he is much better distributor of the ball, and he is more defensively sound (also aggressive). His technique is better, but it's not outstanding. If you had to make a style comparison, maybe a Carrick would fit the bill (pre-2013 season where Carrick was at his best in regards to distribution).
Based on his preseason, Garner is still not looking like he did at youth level in regards to displaying all his tools. He still needs to develop to show the level of passing he did at youth level. However, he will probably show more effort in getting back than McTominay and he does have the potential to develop a good passing game.