There are multiple options for you to do this:
Create a transfer job using the Storage Transfer Service, provided by GCP. Configure this to automatically backup data from one bucket to another. Transfer is a fairly flexible tool and amongst other things, allows you to define files to transfer based on file prefix, modified times or target specific object URLs.
The other way you can do this is to use the gsutil command to copy or sync files from one bucket to another. you could automate this process, add the command as a cronjob on an instance and run it at your chosen times/intervals.
Hope it helps!!
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