It builds builds like a 433 or a 4141 defensively but it will morph into a 2341 as I will show u right away. In this tactic you'll need technical and intelligent players rather than physical players. The only pace based players you'll need are the wingers and the center backs as well cause you will be using an higher defensive line. The DM is your classic number 6 like Busquets, just and intelligent player who can come deep give more confidence on the building up, giving secure lines of pass but also defensively competent with lots of interceptions. Your mezzalas will be someone like Iniesta who give creativity to your game but also likes to assist with killer passes and through balls and will usually find himself to score a few goals. Your wingbacks don't need to be fast paced (although that always helps in every position), they need to be intelligent and good technically but don't need as much creativity, this is a good way to take advantage of some midfielders that are not as good or don't have the flair or the X factor to play on slightly higher positions or even use older wing backs for longer time like Guardiola did with Lahm or Alaba when he adapted him to left back. The CF needs to be exactly that, a forward who can do everything, which is easy to find in the game. (This is my advice, there's no rule for it to work, your choice is *always* the most important.)
Now some explanation on how the tactic works.
This is also good in the press because the match engine in fm21 focus much more on the center play and with tactic you will always have the number advantage on the defensive transition, although you can always tweak the team instructions throughout the game in order to keep a clean sheet or just retain the lead, for example, lower tempo or putting a lower defensive line, its always your choice.
Now a few result i got in half a season as Barcelona and Wolves, both my strikers scored 13 goals in 14/15 games, but Jimenez only in the league and Messi was spread out for all competitions. I also did a fantastic season with benfica losing the final of the UCL but i had few seasons on and the teams was already really powerful so I don't think was as relevant as these results.
In the v2 the wingers are now inverted wingers, which mean the still stay wide to stretch the opp defense but also they try individual opportunities, the dlp is now on support to be more active in the offensive build up, and both mezzalas on attack to attack the half spaces more often and try riskier balls more often. Have fun!