Solved! Go to Solution.
I'm afraid the tool I shared is just not suitable for G703GX unfortunately 😞
It is probably only for Gxx0xGS (e.g. GL703GS, GM501GS etc.).
You need an equivalent version of that keyboard fw update tool for your model (but they are almost impossible to find because are internal laboratory tools and even if you ask ASUS they will simply reply you have to send your laptop in RMA as they can't send you the tool directly)
Just for the chronicles: it just happened again today 27 Oct 2023! A few minutes before there was Windows Cumulative Update KB5030310, but I didn't reboot because I went away... On my return the PC, after sleep + hibernation timeout, had dead keyboard once again (cyclical every ~2yrs?). Dead = not even F2 to access BIOS works at boot and even red power button led is turned off (but this one only still worked of course).
Once again my given solution and that Keyboard FW Update tool fixed the problem.