The solution was to avoid the Signal pin of the Z_PROBE and use the Z_STOP pin. So the cabeling is from:
;### "inductive sensor" -> "duet wifi" ### ;*S*ignal -> Z_STOP ; + -> JUMPER: EXT 5V EN \+5V ; - -> GND (currently Z_POBE)
and is working with the code:
;;; INDUCTIVE ;;; M558 P5 C"!zstop" H6 A5 F120 T20000 S0.07
Took me a long time to understand that "nothing worked(TM)" because of the H argument. It has to be "high" enough to get rid of an G30-"Error: Z probe already triggered at start of probing move"
A F and S are too cryptic documented and have also some side effects to other "self-made commands" ... Just use "trial and error" (1000 times G28/29/30) or googeling for "cut n paste"
BTW the "M558 P1" analog signal mode is at Z_STOP no longer possible use P5 ... "Error: M558: Pin 'zstop' does not support mode analog read"
And do not use any M574 Z1 (Set endstop configuration)
Probably the Z_PROBE_IN input on this board is broken ... I already got my (undocumented(like all other 3D printer stuff)) piezo sensor stuff and after endless tests, measuring and prototyping I got it only running with the usage of the Z_STOP pin.
Maybe it's possible to do a fuction test of Z_PROBE_IN - but who knows...