Yes, all is true except for the de facto part - Queensland calls it a civil partnership. So if I register a civil partnership in QLD could I apply for via 820?I don't really understand your question.
De-Facto for the purposes of immigration is outlined below, if what you are calling civil partnership meets the below then yes you're eligible for an 820 subject tonthe other criteria.
A person is the de facto partner of another person (whether of the same sex or a different sex) if:
they have a mutual commitment to a shared life to the exclusion of all others
the relationship between them is genuine and continuing
they live together or do not live separately and apart on a permanent basis
they are not related by family.