Check the boxes beside Photos and/or Videos, as appropriate.From the “Select Destination” downtown, choose Google Photos.On the next page, you’ll see totals for the numbers of photos, videos, and overall storage in your iCloud Photos Library.
The transfer is done through Apple’s Privacy portal - the same tool that’s been available for a little over two years to download a copy of your data. The new feature, which is highlighted in an Apple support document, appears to be simply the first step toward embracing additional third-party services, noting that it’s “ initially available to customers in Australia, Canada, the European Union, Iceland, Liechtenstein, New Zealand, Norway, Switzerland, the United Kingdom, and the United States for transfers to Google Photos.” This suggests that additional photo services may be coming soon, and it’s likely that for now, Google Photos was both the most popular and easiest choice for Apple to embrace.