The new Australian domain name of .au (compared to the current .com.au) will become available for all on 20th September 2022. There is a possibility of the new domain names becoming a gold rush (or not!)
If your company doesn’t exercise your priority allocation determined by ownership of an existing .com.au or .net.au domain name by the above date then any random person will be able to register the new domain name.
For example if you have greatcompanyname.com.au then anyone will be able to register greatcompanyname.au
This may cause confusion for clients.
See the Australian Government Cyber Security Centre link
https://www.cyber.gov.au/acsc/view-all-content/alerts/are-you-ready-australian-domain-name-changes
If you decide to go ahead and reserve the new domain name it’ll cost around $20/year. The next step if required would involve forwarding your .au website to your .com.au website, or even creating a new website. Changing email addresses is another story altogether.
Just registering the domain name and sitting on it to prevent misuse is the first step
Update: due to high demand here is the initial process.
1. check status at https://www.auda.org.au/tools/priority-status-tool
2. Priority token https://priority.auda.org.au/
3. Apply at registrar e.g. https://ventraip.com.au