Australian immigrants have no criminal record certificate!

Your situation doesn't count. It's just detention and won't be written into your file. So, you can go to the place where your file is located and open a criminal record.

Supplementary answer: It doesn't matter. You can go to the public security bureau to open your criminal record. The foreign party will not check your records from the ID card. The foreigners only look at the criminal records opened by the Public Security Bureau. Where are you from? There is no file in the south. If there is no criminal record, it is opened by the Public Security Bureau. In the north, you can open a certificate and stamp your file. Detention like yours is not a criminal record, it doesn't matter.

You don't need to describe your illegal record this time, because after the public security bureau gives you a certificate, you won't find your other records, so you don't need to say it when you conduct a character test. If you get a visa, as long as it's not in your materials, people won't find it. Rest assured!