On the projects search page of network sites, the default behavior is to only return projects that are associated with places that are descended from the network site place.
Your Cooloola BioBlitz 2021 Collection Project isn’t showing up in the projects page search there because the place Cooloola Bioblitz Study Area doesn’t have a parent place and isn’t being automatically recognized as part of Australia.
However, if you click “view projects from everywhere”, it will turn up.
Or, if you search from the header (click the magnifying glass to open the search box), it will turn up there.
If you edit the place to give it the appropriate parent state, it will be surfaced on the Australia project search page.