'is the Gcode required industry standard or close to it'.
G-code IS an industry Standard: it was defined by NIST after much industry discussion (and some compromises).
(NIST: National Institute for Standards and Technology, USA)

There other languages for CNCs, but they tend to be unique to one vendor. Some of them are a bit weird. A pity for the old vendors who are stuck supporting them: they are in a Catch-22.

NIST G-code is portable across many machine mfrs. That is why it so widely used: like the PC architecture it is open. As to whether it is 'required', that depends on the user, not on the SW.

Cheers
Roger