macOS SparseBundle NAS and Google Coldline Storage Backup Strategy

Question

I currently have a NAS which is configured to act as a network timemachine backup location. Timemachine has completed a successful backup of my macOS laptop to this location and is using it regularly for incremental changes.

I also would like to make an off-site copy of this backup. I was hoping to use a service like google's Coldline storage to maintain infrequent (monthly?) copies of the NAS timemachine files.

Timemachine is storing the backups in sparsebundle files which consists of "bands" of data which AFAIK contain portions of the files being backed up.

If I simply use rsync or rclone type utilities to update the files on the cloud storage, will this result in a recoverable set of data, and how much data can I expect to change in the infrequent remote copies? Ideally I'd like it to only sync the files that have changed between the off-site backups.

Thanks.