Itsme identifies you as a person. You can't have multiple accounts. So a Itsme signature is a proof of personhood (in addition to a proof of identity)
Right. All proofs of identity also act as proofs of personhood, but "proof of personhood" isn't the same. You can have a proof of personhood that doesn't identify which exact person you are.
Indeed! I believe Itsme also has the ability to provide anonymised tokens -- to be able to vote online -- but nobody uses it yet
A UBI coin like WorldCoin needs proof-of-identity as well, to prevent duplicate payouts.
It needs to identify an iris, not anything else about the owner of they iris.
That's not really a meaningful difference, though. It's still an identifier unique to you, and as soon as even a single company can correlate that identifier with any of your other identifiers, the game is over. Your iris now directly identifies you.