PMV (subclass 300 visa) holders can apply to travel to Australia.
The official wording on this is:
If you hold a Prospective Marriage (subclass 300) visa, please be aware that you need to request an exemption from Australia’s travel restrictions and this will be considered on a case-by-case basis.
An intention to marry is not sufficient evidence to demonstrate that you are an immediate family member of an Australian citizen or permanent resident.
You can provide proof of your relationship, or evidence that you meet any other individual exemption category, by applying online at the bottom of this page: covid19.homeaffairs.gov.au
Thank you to those who have sent me a coffee, it is very much appreciated.