I don't see him saying that on reddit, and this appears to be another right-wing conspiracy theory about him[1].

The actual idea, which he doesn't particularly seem to be "pushing", is to have invisible tattoos injected into people in the developing world as an immutable vaccine record, not an ID. It's not unlike the way vets give dogs a small tattoo dot when the dog has been spayed. Medical records don't always survive or travel with patients.

1. https://www.politifact.com/factchecks/2020/apr/09/instagram-...