I haven't tried the Steam version but presumably it works the same and is combining with the EA app? FMT should find Fifa23 from the registry (?)
1. Extract FMT into a folder somewhere (I go with D:\Games\FifaModding and D:\Games\Fifa23)
2. Presumably using the EA App now? You need to "Manage" Fifa23 in there and put -dataPath ModData in the properties like so:
View attachment 191967
3. Run FMT, select Fifa23 and select (Load game let's play with mods)
4. It will now create the SDK, takes a while so go have a coffee (not tea it tastes like piss)
5. When you return from your nice coffee not your disgusting tea you should be sat at the screen where you add mods by clicking import, add some mods.
6. Then click "Launch Game", it will create the mod folder and then launch the EA App and you just play Fifa23 as normal now through the EA App.