Board Thread:Theories and Speculation/@comment-45444155-20200410191621/@comment-6769189-20200427032341

Kaguya used the God Tree/Shinju to turn people into Zetsu. It wasnt until the 4WW that is was stated to be absorbing chakra.

Hagoromo's time and Kaguya's time have overlap so Hagoromo teaching people to use chakra before the Juubi rampage is plausible

I kinda just remembered that Genjutsu basically injects the users chakra into the target. This could have the same effect as Hagoromo's sharing of chakra, linking the targets energies together for the user to control. This may be how Infinite Tsukuyomi worked for Kaguya back in the day