It may take some time depending on the number of files you have and the total size. You can use the "Email me when done" option to get notified once the archival completes. You can then download the created archive locally. Make sure to download it to your Google Drive shared folder or copy it there after download so it gets synced and backed up in the cloud.
YouTube’s mobile app provides controls allowing you to mark a video or playlist for offline playback. With this feature, you can enjoy your favorite clips, music videos and other YouTube content even when your device is without an Internet connection. In this step-by-step tutorial, we’ll explain how to save videos offline, manage your offline and storage settings, access your downloaded videos and more.