Vintage MacBook Pro Backup
How do you back up to iCloud on a MacBook Pro 2009?
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iCloud is not a backup. iCloud is a file syncing service so that multiple devices can access the same data. Plus with all the new security changes it may not be possible for a 2009 Mac to even access some iCloud features (depending on the OS that is installed).
If you want to backup the data on your Mac, then use Time Machine:
Back up your Mac with Time Machine - Apple Support
Even if you are using iCloud you should still be using Time Machine (or some other backup software or method) to have a backup copy of any important data so you have more than one copy of the important data.