The Verdict: Clear Path
You are almost certainly an Australian citizen already, by birth. Apply to Home Affairs for evidence of Australian citizenship, then use it with your birth certificate to apply for a passport.
Until 20 August 1986, birth in Australia made you a citizen whatever your parents' nationality or status. The narrow exception is the child of a foreign diplomat.
One thing to rule out first. If you voluntarily took another country's citizenship as an adult before 4 April 2002, you lost Australian citizenship automatically, without notice. If so, your route is resumption, a separate application with no residence requirement.