Hi. How to backup all photos and videos to iCloud?

What does iCloud back up? - Apple Support

iCloud backup doesn’t include information that is synced and stored in iCloud, like Contacts, Calendars, Bookmarks, Mail, Notes, Voice Memos, Messages*, shared photos, iCloud Photos*, Health data, call history, and files you store in iCloud Drive.

*-If you had turned on Messages in iCloud & iCloud Photos, your content is automatically stored in iCloud and is available on all devices that use the same Apple ID