how to back up my Mac to the apple cloud

Apple does not support macOS backups to iCloud. You can sync files there, but that is nit a strategy for backups, as deleting the file in one place or corrupting it in one place corrupts it everywhere.

Apple provides backups to local storage snd to local network storage, using Time Machine.

… Back up your Mac with Time Machine - Apple Support

There are third-party backup tools, though I am not familiar with the operations particularly around macOs upgrades and restorations. Time Machine is integrated, and documented.