how to backup photos and videos from icloud to reduce space in icloud for new data to backup

Hello sy-icloudbackup,

You can use the steps from this resource to download your photos from iCloud to a device: Archive or make copies of the information you store in iCloud - Apple Support

Once they have been downloaded, you'll also want to turn off iCloud Photos on the device, before attempting to remove any unneeded photos from iCloud. That will make sure that any photos you delete from iCloud aren't also removed for the device. The "How do I turn off iCloud Photos on only one device?" section of this resource has more details on that process: Get help with iCloud Photos - Apple Support

Depending on your current iCloud+ storage plan, you may also be able to upgrade to a plan with more storage: Upgrade to iCloud+ - Apple Support

Hopefully those resources help to further clarify your options.

Take care.