Should you prefer to attack through the middle on the opponent, go for the 4-2-3-1 Narrow. It encourages your wide players to come inside, and it's ideal if you have flying full-backs who like to produce an overlap. Tactically, you shouldn't need to adjust as well a lot, but you may wish for the three attacking midfielders to possess the freedom to switch positions. If so, head to the techniques tab, custom tactic, and change the likelihood creation positioning to cost-free kind. If you want read more FIFA 20 Formations go https://www.u4gm.com/fifa-20-formations

FIFA Expert's recommended work rates and player instructions:
Right Back – Medium Attacking / High Defensive
Left Back – Medium Attacking / High Defensive
Right CB – Low Attacking / High Defensive
Left CB – Low Attacking / High Defensive
Right CDM – Low Attacking / High Defensive
Left CDM – Low Attacking / High Defensive
Right CAM – High Attacking / Low Defensive
Left CAM – High Attacking / Low Defensive
Central Forward/CAM – Medium Attacking / Low Defensive
Striker - High Attacking / Low Defensive

FIFA Expert's recommended (4-2-3-1 Narrow) player instructions:
Right Back – Balanced attack, Normal interceptions.
Left Back – Balanced attack, Normal interceptions.
Right CB – Stay Back, Normal interceptions.
Left CB – Stay Back, Normal interceptions.
Right CDM – Balanced defense, stay back while attacking.
Left CDM – Balanced defense, stay back while attacking.
Right CAM – Stay forward, balanced crossing runs, free roam.
Left CAM – Stay forward, balanced crossing runs, free roam.
Central Forward/CAM – Stay forward, balanced crossing runs, free roam.
Striker - Basic defense support, stay central, get in behind.

Strengths: The deeper lying CAM's allow you to create plenty of chances and with three creative players in here you're going to be a real menace to any opposition. 2CDM's means you have plenty of cover at the back (providing they have decent work rates). The CF and CAM's give the side some width meaning you can still play with a target man upfront. The CF and CAM's should be players with high touch, vision, and creativity. 2 CDM's mean that the full-backs with high attacking WR's can push forward more and give an overlap option. This increases the number of crosses you get in but be wary of tiredness affecting your full-backs if you intend on playing this way

Weaknesses: The considerable downside to this set-up is only having the lone forward lowers the chances to use the 1-2 pass, which is a hugely effective way of playing. Wide areas are a problem sometimes with this set-up, especially as your CAM's and CF will lean towards playing in the center of the pitch. Another problem can be caused by having high attacking work rate full-backs who will push forward too much leaving a lot of space at the back, especially if one or both of the CDM's are going forward too. 

Key player/position: The CAM's and CF. These three players who play in behind the lone ST are key. If you have great chemistry between the three and they can interchange position playing 1-2 passes with each other the movement will be so hard for the defenders to contain.

Most suited style of play: Medium to short passing style. Use a free-form style of play to allow the three players in behind the striker to see the ball in as many dangerous areas as possible.