How can I backup my photos from iCloud?

You need to transfer the documents, data, media files from iCloud to a computer, where you can save them to an external disk.

as described here: Archive or make copies of the information you store in iCloud - Apple Support

If you are using iCloud Photos, it is essential to make regular backups of your iCloud photos, as the iCloud backup of your iPhone will no longer include the photos and videos, when the photos are stored in iCloud, see: iCloud Photos Library: Keep regular backu… - Apple Community

I want to take all photos n videos from iCloud an put it back on iPhone memory