Can I backup (not move) all my files on my mac (documents + all photos, videos, music) using iCloud?

the confusing part is that iCloud is a little bit of both. iCloud backups can be turned on on an iPhone or iPad. The device will then create a backup of any data not already in iCloud for restoration should the device be lost, reset, etc.

but, iCloud is primarily a synchronization service to keep your photos and files in sync across all of your devices. A number of folks use backup liberally but the distinction is important as changes to files in iCloud reflect across all devices immediately, backups are immutable.

so, yes. If someone had your device, and gained access to it by knowing your passcode, they could delete photos, call friends, etc. That’s why Apple encourages using strong passwords and passcodes as well as Touch ID or Face ID. It’s also a reason to keep a backup. It’s improbable that someone would gain access, and they have only 10 attempts before the device is locked. Resetting your device or erasing it through FindMy would not erase your iCloud data, just that on device.

an option may be to enable Time Machine on your Mac to make automatic backups of your system. You can even backup external drives connected to your Mac. The gold standard is 3 copies of your data, made 2 ways, with 1 copy kept offsite. So Time Machine is a good automatic option but you might also add a manual backup from time to time too.

you can load all of your pictures into the photos app too and sync those across devices.

Here are a few ways you can use iCloud to back up the files on your Mac without moving them off your Mac's hard drive:

- Enable iCloud Drive on your Mac. This will sync files stored in iCloud Drive (like Documents, Desktop, etc) between your Mac and iCloud. The files stay on your Mac but are also stored in iCloud as a backup.

- Use iCloud Photo Library to store your photos and videos in iCloud. Like iCloud Drive, the full resolution versions stay on your Mac but are also stored in iCloud.

- Use iCloud Back Up. This backs up settings, apps, and some files, but not your entire hard drive. It's more for disaster recovery than a full backup.

- Use Time Machine to back up to an external hard drive, and also enable Back Up Automatically to iCloud. This will back up your full Mac disk to the external drive, while also doing a more basic iCloud backup.

So in summary, iCloud Drive and iCloud Photo Library can act as a continuous backup of your important files, while also keeping the full versions locally on your Mac. For a full system backup, Time Machine + iCloud Back Up is a good option. Just be aware iCloud has storage limits, so you may need to pay for additional storage for large backups.

Keep in mind that iCloud is primarily a synchronization service, not a backup. While you can sync photos, music, and file to iCloud through your Mac, you're not making a backup of the files. Should you delete a file, it is deleted everywhere. And, should you need to restore more than files to your computer, or if you accidentally give a device to someone who permanently deletes files or photos, you'll appreciate having a solid backup.