ECG app in Australia

No one here would know the answer to that question. This is a user to user support forum and Apple does not participate here. Apple does not share information on their business dealings until they release a press release. They need government approval for a medical device, and obviously do not have that at this time.

As far as your statement about paying for Watch, in all advertisements for the Apple Watch, it states that some features are not available in all locations, especially the ECG.

There is a very long thread on this subject with lots of upset Australians. But if you read the thread, and do not get carried away with all the complaints, you will find that the issue is the TGA's rules do not allow the Apple Watch ECG, as currently implemented, to be approved.

https://discussions.apple.com/thread/251543352

There are rumors that in February 2021 the rules may change to include the Apple Watch ECG, but Crystal Balls are notorious for being wrong about the future.