The ability to share your AirTag's location is available in "most regions worldwide" as part of the iOS 18.2 public beta. If you don't have the beta, Apple plans on rolling out the update to all users with an iPhone X or later "soon." MacRumors reported on the capability in the second developer beta of iOS 18.2 last week.
As part of the rollout, Apple is partnering with over 15 airlines, including Delta, United, Virgin Atlantic, Lufthansa, Air Canada, and more. All of these airlines will be able to "securely" accept links to lost items, as "access to each link will be limited to a small number of people, and recipients will be required to authenticate in order to view the link through either their Apple Account or partner email address." This feature will be available in the "coming months."