How can I backup my MacBook pro to iCloud?

Macs do not back up to iCloud. Use Time Machine (or similar) to backup instead.

Back up your Mac with Time Machine - Apple Support

keep in mind iCloud on your MacBook pro is a sync service, not a backup-tool. This means that if you e.g. sync your photos to iCloud and you delete one on your MacBook, it will be deleted in iCloud too. The same for e.g. files in iCloud drive.

The advantage of a sync-service is that you you can manage files, emails, photos, notes, .. on all your devices when logged in in iCloud (e.g. iPhone, iPad, iMac, MacBook)

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