You can use the Google Takeout service to automatically transfer all your photos and videos from your Google account to your Flickr account. All the photos transferred to your Flickr account will be set as private for which you can manually change the permissions. There is also another method wherein you need to manually download the photos from Google photos and then manually upload them to your Flickr account, this is a time-consuming process, therefore, Takeout is the best choice to bulk transfer the media to your Flickr account.
Steps to Transfer Photos from Google Photos to Flickr Account
Here are the Simple Steps to Move Google Photos to Flickr Account Using Google Takeout Service.