The first two conditions for using AirPods hearing aid functionality are fairly easy; these are:

1. Second-generation AirPods Pro (both Lightning and USB-C versions are compatible)

2. An iPhone or iPad running iOS 18.1

Similar to Google's geographically limited feature rollouts, it's been seen on Apple's website (by 9to5Mac) that the new Hearing Health features for AirPods Pro 2 will be initially available only in a couple of countries. Those countries are the USA and Canada. That means the third condition is:

Despite the global popularity of AirPods, users outside North America will have to wait, for I-don't-know-how-long, to experience the new Hearing Health capabilities.

The functionality the rest of the world will be missing out on would be:

Apple's decision to restrict the feature's availability most p[probably stems from regulatory hurdles. The company has secured FDA authorization in the US and Canada, allowing them to market the AirPods Pro 2 as hearing aids. Similar approvals from health regulators in other countries are presumably pending, which explains the limited rollout.

Apple hasn't provided a timeline for international expansion.