The last version of SpecialK to work with FF12 is 0.9.23. The 0.10.x versions nor due any of the post-exile-from-Steam versions. Additionally, for local injection, you have to name the dll dinput8.dll. I actually figured this out because the FF15 version of SpecialK (which is forked from 0.9.22) has the same quirk. That might also mean the FF15 version of SpecialK is better for this, but I’m not sure.
I haven’t really dared to try the advanced settings like flip discard, I mainly just wanted to inject SpecialK for the QoL settings like the volume manager (because the game often ignores the audio settings for certain things and the Windows volume mixer just sucks).
I’m guessing other FF PC ports probably have issues. It would be good if the current SpecialK was updated to work with them.