Apple Launches Service for Transferring iCloud Photos and Videos to Google Photos
As outlined in an Apple support document, you can go to Apple's privacy website and sign in to see the "Transfer a copy of your data" option. If you select this and go through all the steps, Apple will transfer your iCloud photos and videos to Google Photos.
Transferring photos and videos from iCloud Photos does not remove the content you have stored with Apple, but it provides a backup method and stores a copy of the content on Google Photos.
The transfer process takes between three and seven days, with Apple verifying that the request was made by you. To do the transfer, you must have two-factor authentication turned on for your Apple ID account and you must have a Google Photos account with enough storage to complete the transfer.
Smart Albums, Live Photos, photo stream content, some metadata, and some RAW photos are not able to be transferred, but formats including .jpg, .png, .webp, .gif, some RAW files, .mpg, .mod, .mmv, .tod, .wmv, .asf, .avi, .divx, .mov, .m4v, .3gp, .3g2, .mp4, .m2t, .m2ts, .mts, and .mkv are compatible.
Only the most recent edit of a photo is transferred rather than the original version, and duplicates appear as just one photo. Images are transferred in their albums whenever possible, but videos are transferred separately.
Apple's transfer service is available to customers in Australia, Canada, the European Union, Iceland, Liechtenstein, New Zealand, Norway, Switzerland, the United Kingdom, and the United States at this time.