Understandably, I think there is a bit of confusion here between IATA and ICAO.
IATA is the International Air Transport Association, which is a trade association of the world's airlines, supporting technical and operational safety standards. They developed the IATA Travel Pass referenced above.
ICAO is the International Civil Aviation Organisation, a specialised agency of the United Nations, funded by 193 contracting states, which oversees the development of standards and recommended practices for civil aviation globally. National aviation regulators such as CASA adopt and comply with most of these standards.
Confusingly, Australia's new International Digital vaccination certificates are issued to comply with the VDS-NC QR code standard for cross-border verification certificates, which is issued by ICAO.
I hope that helps.
tb