Unfortunately, there is no definitive date on when Australia’s borders will open to international travel worldwide. However, airlines like Qantas do not plan to resume their international travel flights until October 2021. There may be border closures in place until a nationwide vaccination program is enacted.
A travel bubble with New Zealand already opened on 19 April 2021.
I would advise you to keep a look into the open borders live news resources that has details about borders and much more:
You can also find the official advise from the government on this https://covid19.homeaffairs.gov.au
Hope it helps!