There is no "unbeatable" tactic — the FM26 match engine is too dynamic for that. But the closest thing right now based on TFF's 75 Siblings's 2,700-match testing (Patch 26.3.0) is ZaZ - Autumn 3.39 ST in a 4-2-4 shape: 80.0 PTS/season, +45 GD, 93 goals scored.
The reason 4-2-4 is dominating the meta isn't just the formation — it's that the engine currently rewards pace + direct transitions more than possession. If you want to build your own variant, the three non-negotiables are:
High press + Counter-press (the strongest instruction combo, community consensus)
Pace/Acceleration 14+ on all front 4 + both full-backs
Two DMs on support, not defend — they're your transition shield
What team are you managing and what's your budget? 4-2-4 needs a specific player profile to work — happy to suggest alternatives if you're playing a mid-table side.