Thank you SO much for providing me the solution and for handling the documentation update! I have tested and verified it as well.
Sidenote. My hopes were that muting all four FX would exploit the same “feature” that pressing MUTE ALL FX in MixPad has, that is, toggling also inserted FX to OUT. But it seems that will have to wait for Add softkey function to toggle inserted FX IN/OUT or an extended MIDI implementation.