No, you cannot select both. When setting up or updating your scanner’s client parameters in Client tab > Client Location, you can select client parameters either by Countries or Regions, but not both.

For example, if you want to search for a location such as Australia, you can select it from the listed Countries list or you could just select the region such as Oceania (which includes Australia, Vanuatu, Kiribati, Marshall Islands, Nauru, New Zealand, Palau, Papua New Guinea, Samoa, Solomon Islands, Tonga, Tuvalu, Federated States of Micronesia, and Fiji) from the Regions list.
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Selecting a region, will include all the countries within that region in your scanner’s search results. For a list of countries included in each region, see List of countries by regional classification - Meta (wikimedia.org).