Unfortunately the Country Filter in the Azure AS Sign in Logs is hard match , ( not contains )

So you either have to download the logs to Excel and use filtering in there

You can download and filter in Excel.

Or use the Log Analytics workspace where the Azure AD sign in Logs https://learn.microsoft.com/en-us/entra/identity/monitoring-health/howto-integrate-activity-logs-with-azure-monitor-logs are going to query this with country code

SigninLogs
| where (LocationDetails["countryOrRegion"]) == "AU"