Not everyone is allowed to leave Australia during the COVID travel ban period.
A resident of Australia is not allowed to leave the country unless they havevan exemption.
A Non Resident is permitted to leave.
What is the definition of Non Resident?
According to one source, someone who successfully departed Australia, the definition of ‘not resident’ was “anyone who, in the last 12 months prior to departure date, had spent more days outside Australia than in.”
This appears to say that those on a temporary visa, who have spent over 6 months on Australia, during the last 12 months, are treated as resident for this purpose, and would need an exemption to be able to leave.
However, this site https://covid19.homeaffairs.gov.au/leaving-australia says:
Temporary visa holders do not need an exemption to depart Australia. They can leave at any time, as long as border restrictions in their home country allow them to return.
It also says: If you are an Australian citizen or a permanent resident you cannot leave Australia due to COVID-19 restrictions unless you have an exemption.
And goes on to say: You are exempt if you are ordinarily resident in a country other than Australia.
That last part seems to agree with the earlier statement of 6 months in one year.
This clarifies that a temporary visa holder, even of residing in Australia long term, is allowed to leave, without needing an exemption.
Some Visa Applicants might find an Experienced Australian Migration Agent of great assistance.