Disclaimer
Yes, I also submitted enquires to expert services, keen to discuss this here to see if anyone here had or friends heard of have done this in the past.
The scenario is,
An individual has Australian and other country (N) citizenship that doesn't allow dual citizenship.
The goal is to enable this individual to travel to and from to country N without N knowing its Australian citizenship.
The assumption is
Leaving Australia to country N using country N passport should be fine as AU airport confirms the individual has the right to enter the country
The challenge is
Returning Australia from country N using country N passport will require a legal visa to enter Australia
The question is
Could this individual apply travel visa 600 from country N passport when it also hold Australian citizenship?
From homeaffairs website, there is no eligibility statement that AU citizen can't apply 600, unlike 155 or 157 that highlight AU citizen can't apply.
The only catch is the 8558 condition - Non Resident: Cannot stay for more than 12 months in any 18 month period.
Many thanks
You need to talk to a immigration lawyer