Australia is an island, the only reason the USA is not an island like you mentioned in an above comment is because it is touched by other countries. Australia has no borders.
To everyone, whenever you make a comment, check the information beforehand. It is commonly accepted that Australia is a continent. I was hoping not to have to go this far, but here are a few trustworthy sources, which prove this: https://www.britannica.com/science/continent
According to Wikipedia, "Australia, officially known as the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands." As it consists of a continent, it is not an island. I agree with Nathaniel for this.
Also Qatar is an island
https://www.nationalgeographic.org/encyclopedia/Continent/
https://dictionary.cambridge.org/de/worterbuch/englisch/continent